THE GEOLOGY OF THE LAKELAND FINLAND AREA

Transcription

1 THE GEOLOGY OF THE LAKELAND FINLAND AREA Jari Nenonen and Anne Portaankorva Geological Survey of Finland 2009

2 2 TABLE OF CONTENTS 1. FINLAND S GEOLOGICAL HISTORY BEDROCK GEOLOGY OF FINLAND AND THE NEED-PROJECT S REGION 4 3. THE BEDROCK OF THE NEED-PROJECT S REGION SURFICIAL DEPOSITS IN THE NEED-PROJECT REGION Glacial deposits Basal till Ablation moraine hummocky moraine Glaciofluvial deposits Eskers Ice-marginal formations Aeolian deposits Peat deposits EVOLUTION OF THE LAKES GEOLOGICAL SITES IN NATURE TOURISM LITERATURE

3 3 1. FINLAND S GEOLOGICAL HISTORY A special feature in Finnish geology is the very old bedrock and the much younger surficial deposits lying on top of it. Finland s geological history is extremely long. The history of bedrock goes up to 3,5 3,7 Ga ago when the old Archaean basement was developed(fig. 1). The oldest stone in Finland and in the whole of the EU is Siurua gneiss (3,5 Ga years old) near the town of Pudasjärvi in northern Finland (Fig. 2). Surficial deposits have developed during the last two million years, during the so called ice age. Glaciers eroded the bedrock beneath them and deposited loosened material upon it as quaternary deposits. Bedrock, together with quaternary deposits and landforms, builds up the variable landscape complex which can be seen today. Figure 1. Two scales illustrating the historical development of Finnish geology by Tapani Tervo and Harri Kutvonen, GTK.

4 4 2. BEDROCK GEOLOGY OF FINLAND AND THE NEED-PROJECT S REGION THE ARCHEAN BASEMENT The bedrock of Eastern and Northern Finland consists of ancient rocks dating back to more than 2500 million years, the detailed origins of which are not accurately known. Their development would seem, however, to have been controlled by events in which large quantities of the earth s crust melted and then crystallized slowly to form various granitoids and gneisses (Fig. 3). These were interspersed with sequences of schists, depicted in a darker shade on the map, which represent the remnants of rocks that had once been deposited at the surface, mostly from thick, widely distributed lava flows. This Archean area is, in effect, an ancient continent that served as a starting point for the second stage in the development of the Finnish bedrock (Map 1). Figure 2. The Siurua gneiss (age 3,5-3,7 Ga) Map 1. The Archean basement Figure 3. Gneiss

5 5 THE KARELIDIC BEDROCK The creation of the Archean bedrock was followed by more than 500 million years of erosion and deposition that caused clay, sand and gravel to accumulate on top of the ancient continent and at its edges. These gave rise in time to the quartzites, conglomerates, mica schists, mica gneisses and granulites of the Karelidic belt (Fig. 4, 5). During this period the earth s crust was broken up by numerous rift valleys bounded by fault zones. The faults were filled with molten rock, or magma, some of which crystallized deep in the crust, while some was discharged at the surface to form sequences of volcanic rocks. These are marked in dark green on map 2. Then, about 2000 million years ago, the ancient continent split in two and the blocks drifted apart causing the fault to develop into an ocean. It is not known what happened to the western block. Figure 4. Ripple marks in quartzite Map 2. The Karelidic bedrock Figure 5.Granulite

6 THE SVECOFENNIAN BEDROCK 6 Already about 1920 million years ago, the present area of Eastern Finland was an ancient continental land mass covered by sedimentary rocks, with an ocean to the west of it. As a result of movements of the tectonic plates, a number of arcs of volcanic islands arose that were thrust eastwards by flows taking place within the earth, colliding with each other and eventually with the old Archean basement. By the time this collision phase had come to an end around 1870 million years ago, the area of Finland was occupied by a range of high mountains( Map 3). The processes of folding that gave rise to these mountains, had caused the volcanic islands and their related sedimentary rocks to be piled up against the ancient continental mass in the east. This meant that some of the sedimentary rocks were thrust down deep into the earth s crust, where they melted and then slowly crystallized to form various plutonic rocks (Fig. 6, 7). Figure 6. The Nattanen granite tor formations Map 3. The Svecofennian bedrock Figure 7. Koli quartzite polished by continental ice

7 YOUNGER FORMATIONS 7 The folding that created the range of mountains was followed by a long period of erosion, so that only a few isolated features of the Finnish bedrock have been preserved from that time. These rapakivi granite areas are indicated in red on the map 4 (Fig. 8), while the yellow areas show the presence of sandstones and argillites dating back million years. The events that gave rise to the Caledonides in Norway about million years ago also caused a bed of younger sedimentary rocks to thrust into the northwestern parts of the Enontekiö region of Finland. A number of kimberlite pipes of igneous origin that contain diamonds, have been discovered in Northern and Eastern Finland (Fig.9), and the hills of Iivaara and Sokli are formed by alkaline igneous rocks aged million years. Figure 8. The Rapakivi granite, GTK. Map 4. Young bedrock formations. Figure 9. Diamonds and side minerals. GTK Development of Finnish bedrock presented on same time scale.

8 NEED-region 8

9 9 3. THE BEDROCK OF THE NEED-PROJECT S REGION In the area under study, the bedrock is divided into three bedrock units of different ages. The northernmost is the Archean gneiss area (age Ma), in the center is theearly Prorerozoic schist and plutonic rock area (age Ma) and in the south the Middle Proterozoic rapakivi area (age Ma) (Map 5) (Vaasjoki ym. 2005). The northernmost, Archean area, belongs to Finland s oldest bedrock area. Typical types of rocks in that area are gneisses with greenstone periods. The Archean mountain folding was followed by hundreds of millions of years of erosion, which involved strong faulting and volcanism. The bedrock were splitting strongly, forming sedimentation basements and there was also active volcanism at that time. At the end of the splitting phase major climate changes occurred, the most significant being the increase in the amount of oxygen ca 2100 million years ago to the current level (Karhu 1993). About 2400 million years ago the mountain ridge was eroded into a flat peneplain. Thick sediments were deposited on top of it about million years ago. Sedimentation was associated with several periods of volcanism which resulted in diabase veins cutting the Archean basement and the sediments about million years ago (Fig. 10) (Vaasjoki ym. 2005). The long sedimentation phase was followed by the folding of the Svecokarelian mountains about million years ago. The sediments were folded and metamorphosed as crystalline schists like quartzite, phyllite and mica schist. Primary structures like ripple marks in the Koli quartzites can still be seen in the rocks (Fig 11).

10 Map 5. The bedrock of the NEED region, GTK. 10

11 Figure 10. A series of illustrations showing the development of eastern Finland and the Koli area s bedrock. T. Tervo, GTK 11

12 12 Figure 11. Quartzite with ripple marks. A. Portaankorva, GTK. Tectonic movements in the earth crust s ended about 1800 million years ago, and was followed by a long phase of erosion. In the southernmost part of the area fine grained rapakivi rocks can be found. This rapakivi bedrock is aged about million years. (Simonen & Tyrväinen 1981) During the Precambrian eon many meteorites crashed in to the earth. The big meterorite crater, Paasselkä, can be seen today as a rounded lake in the eastern part of the area (Fig. 12) (Kuivasaari ym. 2000). Figure 12. Paasselkä, meteorite crater. A. Portaankorva.

13 13 Tectonic movements created fault and fracture zones in the bedrock. The Kolvanauuro and Korkiakoski gorges are situated in these kind of fault zones (Fig 13, 14). Later the ice age and melting waters cleaned the loosened stone and earth material out from the gorges and made them clearer. The fractured outlook of the bedrock is clearly visible in the mosaic like landscape of Saimaa Pielinen lake. Erosion is active all the time and different kinds of erosion forms can be seen in the area, e.g. boulder fields and caves (Kuvaanniemi cave). Figure 13. Kolvananuuro gorge. Photos: A. Portaankorva, GTK Figure 14.. Korkeakoski gorge and rapids. 4. SURFICIAL DEPOSITS IN THE NEED-PROJECT REGION Finland is the daughter of the ice age. During the last 2,5 million years, several glaciations have shaped today s landscape. Eastern Finland s quaternary deposits were deposited during the late- Weichselian glaciation. The Scandinavian ice sheet reached its maximum size about years ago (Lunkka 2007), then as a result of global warming, the glacier began to melt, and its edge reached the southern coast of Finland about years ago (Donner 1995). (Fig. 15) During the melting phase, the continental ice sheet was divided into ice lobes which in turn again diminished into smaller, independently operating sub lobes. During the last glaciation there were two ice lobes, Lake-Finland and the North Karelian lobes. The situation of these ice lobes can easily be seen in the form of the Salpausselkä end formations. (Punkari 1978).

14 14 According to striations and the direction of the elongated landforms e.g. drumlins, the continental ice flowed from northwest to southeast, but during the melting phase directions of theflow vary. In the eastern and northern parts of the area the flow was directed from northwest to the southeast while in the southwest parts, from west-northwest to east-northeast (Map 6). Figure 15. Distribution of the Weichselian glaciation front margins and the ages of the ice front retreat. T. Tervo, GTK

15 Map 6. Directions of the continental ice flow in Finland. 15

16 16 QUATERNARY DEPOSITS OF FINLAND NEED-region

17 17 JUUKA KOLI RANTASALMI LEIVONMÄKI Map 7. The Quaternary deposits of the NEED-project region

18 Glacial deposits The area s most common glacial deposit type is till, which is unsorted drift loosened from the bedrock and transported by the continental ice sheet. The grain size of till varies from clay to boulders and it covers the bedrock in variable thicknesses. Till is deposited in different kinds of landforms such ass drumlins and hummocky moraines (Map 7) Basal till Basal till was deposited under the glacier. It is well graded and compact. Orientation of the elongated stones in basal till is parallel to the movement of the glacier. Basal till is the predominant sediment type in the area, and often act s as substratum for other sediments. In areas where the continental ice sheet flowed rapidly, it has formed basal till streamlined formations, drumlins. They are elongated ridges parallel with the direction of the continental ice flow. Drumlins were deposited under the glaciers, often to the distal side of a bedrock obstacle and they usually occur as large drumlin fields. (Fig 16-18). Figure 16. Origin of the drumlins. Harri Kutvonen,GTK Figure 17. Drumlin field. Figure 18. Drumlin ridge. A. Portaankorva,GTK

19 19 Drumlin fields are situated in the eastern and western part of the area. The most significant drumlin field of the area is that of Pieksämäki parts of which reach to the western part of the area under study. Drumlins have been deposited at the birth of Salpausselkäs and their fan-like orientation reflects the direction of the advancing of Lake Finland ice lobe. (Glückert 1973, Mäkinen ym.2007) End moraines were deposited at the margin of the continental ice. They indicate the ancient front of the ice sheet. Small end moraines, called De Geer moraines, occur in swarms indicating the position of the front of a step-wise retreating ice sheet. Small end moraines occur in the NE corner of the area. Large end moraines occur in the zone of Salpausselkä II. The Koitere and Pielisjärvi end moraines in the NE part of the area are the biggest example of these (Map 7) Ablation moraine hummocky moraine Ablation moraine is made of loose till which is coarser than basal till, often containing abundant sorted material which is strewn with cobbles and boulders. Ablation till occurs as a thin blanket on basal till. When in thick layers of independent forms it is called hummocky moraine (Fig ). These occur in large fields of usually non oriented ridges or hills and the most significant hummocky moraine fields are situated in the eastern part of the area. Figure 19. Deposition of hummocky moraine. Figure 20. Cross section of hummocky moraines. J. Nenonen, GTK Harri Kutvonen, GTK.

20 20 Figure Smooth shaped hummocky moraines. A. Portaankorva, GTK Glaciofluvial deposits Glaciofluvial deposits are formations deposited by meltwaters either under, in, on, or at the front of melting continental ice. The origin of the material in them is from the glacier itself or from beneath it. Meltwaters have washed and rounded the grains and sorted them into layers of different grain size Eskers Eskers were deposited at the melting stage of the glacier. They were deposited in crevasses and tunnels in the continental ice sheet. Eskers are seen on the map as long chains (Fig. 23). The orientation of the eskers indicates the direction in which the meltwater ran. In this area the most common direction of eskers is from northwest to southeast. The orientation is perpendicular to the orientation of marginal formations e.g. Salpausselkä I, II. Eskers are usually steeply sloping, continuous, smoothly winding ridges (Fig. 24). They most often consist of sandy and gravelly material although cobble and boulder material may occur the in deep core. Eskers form a big ground water reserve in Finland. Figure 23. Origin of esker and kettle holes. Harri Kutvonen, GTK.

21 21 In the region under study, eskers are found in the eastern part of Salpausselkä and in the North Karelian marginal formations. The sandy formations connected to Salpausselkä ice marginal formations are deltas, which were deposited in deep water in front of the melting water tunnels. Some of them have continued sedimentation above the surface in the form of sandurs dry land deltas. (Donner 1995) Figure 24. Metelinharju esker. A. Portaankorva, GTK. The early phases of the Baltic Sea eroded the slopes of the eskers and ice marginal formations and re deposited the material in to littoral deposits of varying raised beaches Ice-marginal formations Ice-marginal formations are complex combinations of deltas and end moraines in which sorted sediments dominate but till is also common. Due to the occasionally colder climate, the retreating of the continental ice stopped during the Younger Dryas stage about years ago. At that time the large Salpausselkä I, II ice marginal formations were deposited in the front of Lake Finland ice lobe (Fig. 25, 26) (Saarnisto & Saarinen 2001). Salpausselkä I was deposited about years ago. Salpausselkä II was deposited years ago km NW from Salpausselkä I. The North Karelian ice lobe was situated to the north from the Lake Finland ice lobe. Due retreat of the ice lobe, only small and discontinuous ice marginal formations were deposited. to the rapid

22 22 Figure 25. Kylänniemi, Salpausselkä II, ice marginal formation. A. Portaankorva, GTK. Figure 26. Origin of ice marginal formation. H. Kutvonen,GTK

23 23 Map 8. Ice marginal formations. H. Kutvonen, GTK. To the northeast of Salpausselkä, ice marginal formations continue into the Koitere ice marginal formation which is part of the Rukajärvi formation on the Russian side. To the northwest from the Koitere ice marginal formation the Pielisjärvi marginal formation is to be found. The most distinguished part of it is the Jaamankangas ice marginal delta (Map 8) Aeolian deposits Dunes or drifts of aeolian sand are composed of material derived from sorted sediments of glaciofluvial or littoral origin. Material is fine sand, redeposited by wind and forming single dunes, dune chains or large dune fields (Fig 27, 28). Fine grained dust transported by wind has been deposited as a thin loess deposit e.g. in North Karelia. The most significant dune areas are connected with big eskers, interlobate formations or ice marginal formations.

24 24 Figure 27. Origin of dunes. H. Kutvonen,GTK. Figure 28. Fossilized dunes. A. Portaankorva, GTK Peat deposits Peat deposits are formed from the humified remains of mire plants and peatlands often follow the morphology of the ground surface. The Eastern Finland peatlands are situated near marginal and moraine formations (Map 7). Deposition of the peat began immediately after the waning of the continental ice. The oldest peat deposits in the area are situated in the southern parts of North Karelia. (Virtanen ym. 2003) 5. EVOLUTION OF THE LAKES The lakes in the area were part of the Baltic Sea basin in the early post-glacial period, but were isolated from it by land uplift (Fig 29, 30). The lakes have acomplex history, having changed in shape, size and outlet location along with shifts in the rate of uplift from northwest to southeast. (Pajunen 2005) The evolution of lake Saimaa was very complex. The oldest drainage channels were at the end of the lake where the most rapid uplift took place. The water level in the lake began to rise and all the independent lakes in the south were submerged. At the same time a new drainage channel opened up in the southwest. The shore level that developed before the opening of the Vuoksi channel about years ago, is the highest of the ancient Great Saimaa shores. The river Vuoksi was formed when the waters of Great Saimaa carved a channel through Salpausselkä I to lake Ladoga (Map 9). Lake Pielinen became isolated from the Baltic Sea over years ago (Fig. 31,32). (Saarnisto 1970, Pajunen 2005).

25 25 Figure 29. Rates (mm) of land uplift in Finland Figure 30. Land uplifting phenomena. H. Kutvonen, GTK

26 26 Figure 31. Small river potholes at the bottom of Imatra rapids. A. Portaankorva, GTK. Figure 32. The early Great Saimaa shore levels are still clearly visible. A. Portaankorva, GTK.

27 Evolution of the lakes in eastern Finland (Hannu Pajunen, GTK) 27 Situation 9500 years ago, formation of the Great Saimaa lake begins. - vedenpinta kohoaa luoteeseen laskevissa järvissä - järvet laajenevat ja vesi syvenee - erilliset järvet yhtyvät ja suurjärvi alkaa muotoutua Situation years ago, maximum extent of the Great Saimaa lake. - muinaisen Suur-Saimaan maksimivaihe - järvi laajimmillaan ja syvimmillään - lasku-uomat Pielavedellä ja Ristiinassa Present time, The Great Saimaa lake is shrinking and splitting up to smaller lakes - vedenpinta alenee kaakkoon laskevissa järvissä - järvet pienenevät ja vesi mataloituu -muinainen suurjärvi pilkkoutuu erillisiksi altaiksi

28 Map 9. Great Saimaa and lake Päijänne in their biggest. 28

29 29 6. GEOLOGICAL SITES IN NATURE TOURISM Nature has a lot of magnificent places and sites made by geological processes and all too often we don t think about or know the interesting history or stories behind them. Geological sites provide tourism entrepreneurs new opportunities to diversify their programme selection and the sites they visit. With combining information about the history or nature/ geology of the area, with stories and beliefs to the places visited creates interesting and attractive experiences for tourists. Figure 33. Porosalmen stone cave, Rantasalmi. Figure 34. Cave and old habitation near Puumala village. A. Portaanorva, GTK. The NEED project region includes target areas such as the Koli national park and its national landscape, Finland's Stone centre in Juuka, the geological paths of Rantasalmi and the national park of Leivonmäki with its nature routes (Maps 7,10). In themselves, these places are significant, interesting natural and geological sites. Many other significant geological sites are also situated in the beautiful lake district of Saimaa-Pielinen, e.g. the Punkaharju esker, the Salpausselkä ice-marginal formations and the Imatra rapids. Almost none of the sites have been used to meet the needs of the regional nature tourism. They are still a valuable unused resource for the development of tourism (Map 10).

30 30 JUUKA KOLI RANTASALMI LEIVONMÄKI Map 10. Geological sites mapped in the region under study (Portaankorva 2009).

31 31 7. LITERATURE Donner, J The Quatenary History of Scandinavia. Cambridge University Press. 200 s. Glückert, G Two large drumlin fields in central Finland. Societas Geographica Fenniae. Fennia 120. Vammalan kirjapaino Oy. 37 s. Haavisto-Hyvärinen, M., Kielosto, S., Niemelä, J Precrags and drumlin fields in Finland. Sedimentary Geology Karhu, J.A Paleoproterozoic evolution of the carbon isotope ratios of sedimentary carbonates in the Fennoscandian Shield. Geological Suvey of Finland. Bulletin 371, Karhu & O`Brien Microfossil-like tourmaline microlites in early proterozoic nodular chert at Kiihtelysvaara, Eastern Finland. Bulletin of The Geological Society of Finland. Number 64, Part 1. Kuivasaari, T., Pesonen, L. J., Elo, S., Plado, J., Lehtinen, M Paasselkä - the ninth meteorite impact structure in Finland. In: Meteorite impacts in Precambrian shields, May 24-28, 2000, Lappajärvi- Karikkoselkä-Sääksjärvi, Finland : programme and abstracts. Espoo : Helsinki: Geological Survey of Finland : University of Helsinki, 79 s. Lunkka, J.-P., Johansson, P., Saarnisto, M., Sallasmaa Glaciation of Finland. In: Ehlers, J & Gibbard, P.L. (editors). Quaternary Glaciations Extent and Chronology. Elsevier Luukkonen, E.J. & Sorjonen-Ward, P Arkeeinen kallioperä ikkuna 3 miljardin vuoden taakse. Teoksessa: Lehtinen, M. Nurmi, P. Rämö, T Suomen kallioperä 3000 vuosimiljoonaa. Gummerus Jyväskylä Lyytikäinen, A., Kontturi, O Pohjois-Karjalan harjuluonto. Valtakunnallinen harjututkimus. Raportti 13. Joensuu. 112 s + liitekartta. Mäkinen, K., Palmu, J-P, Teeriaho, J., Rönty, H., Rauhaniemi, T., Jarva, J Valtakunnallisesti arvokkaat moreenimuodostumat. Suomen ympäristö 14/2007. Ympäristöministeriö. 120 s. + DVD Pajunen, H Ala-Saimaan sedimentaatioympäristön muuttuminen jääkauden jälkeen. Terra 117: 1, Pekkarinen, L.J., Kohonen, J., Vuollo, J., Äikäs, O Kolin kartta-alueen kallioperä. Suomen geologinen kartta. Kallioperäkarttojen selitykset. Lehti Geologian tutkimuskeskus. Espoo. 116 s. Portaankorva, A Geologisten kohteiden luokittelu ja hyödyntäminen luontomatkailussa. Pro gradu-tutkielma. Oulun yliopisto. Geotieteiden laitos. 87 s. Punkari, M Suomen glasifluviaalisten ja muiden glasigeenisten suurmuotojen tulkinta Landsatsatelliittikuvista. University of Helsinki. 71 s. Rainio, H The Younger Dyas ice-marginal formations of sothern Finland. In: Eastern Fennoscandian Younger Dryas end moraines. Rainio, H. & Saarnisto, M. (eds.). IGCP Project 253, Termination of the Pleistocene. Field conference North Karelia, Finland and Karelian AASR. Opas

32 32 Rainio, H Late Weichselian end moraines and deglaciation in Eastern and Central Finland. Geological Survey of Finland. Espoo Rainio, H., Saarnisto, M., Ekman, I Younger Dryas end moraines in Finland and NW Russia. Quaternary International, Vol Saarnisto, M The Late Weichselian and Flandrian history of the Saimaa lake complex. Societas Scientiarum Fennica, Commentationes Physico-Mathematicae, s. Saarnisto, M Chronology of the Salpausselkä end moraines in Finland, and the fluctuation of Baltic ice lake levels. In: Eastern Fennoscandian Younger Dryas end moraines. Geologian tutkimuskeskus. Opas Saarnisto, M. & Salonen, V-P Glacial history of Finland. In: Ehlers, J., Kozarski, S., Gibbard, P. (editos). Glacial deposits in North-East Europe. A.A.Balkema, Rotterdam, Saarnisto, M. & Saarinen, T Deglaciation chronology of the Scandinavian Ice Sheet from the Lake Onega Basin to the Salpausselkä End Moraines. Global and Planetary Change. Volume 31, Issues Simonen, A. & Tyrväinen, A Kallioperäkartan selitys, lehti Savitaipaleen kartta-alueen kallioperä. Geologinen tutkimuslaitos. Espoo. 29 s. Tynni and Sarapää Fossil Bacterial forms in early proterozoic dolomite at Kiihtelysvaara in Eastern Finland. Bulletin of The Geological Society of Finland. Number 59, Part 2. Vaasjoki, M, Korsman, K., Koistinen, T Overview In Lehtinen, M., Nurmi, P.A., Rämö, O.T. (toim.) Precambrian geology of Finland. Key to the evolution of the Fennoscandian Shield. Developments in Precambrian Geology 14. Elsevier. 701 s. Virtanen, K., Hänninen, P., Kallinen, R-L., Vartiainen, S., Herranen, T., Jokisaari, R Suomen turvevarat Geologian tutkimuskeskus. Tutkimusraportti 156. Espoo. 100 s + liitteet.

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