An approach to palaeoseismicity in the Olkiluoto (sea) area during the early Holocene

Olkiluoto Island is situated in the northern Baltic Sea, near the southwestern coast of Finland, and is the proposed location of a spent nuclear fuel repository. This study examined Holocene palaeoseismicity in the Olkiluoto area and in the surrounding sea areas by computer simulations together with acoustic-seismic, sedimentological and dating methods. The most abundant rock type on the island is migmatic mica gneiss, intruded by tonalites, granodiorites and granites. The surrounding Baltic Sea seabed consists of Palaeoproterozoic crystalline bedrock, which is to a great extent covered by younger Mesoproterozoic sedimentary rocks. The area contains several ancient deep-seated fracture zones that divide it into bedrock blocks. The response of bedrock at the Olkiluoto site was modelled considering four future ice-age scenarios. Each scenario produced shear displacements of fractures with different times of occurrence and varying recovery rates. Generally, the larger the maximum ice load, the larger were the permanent shear displacements. For a basic case, the maximum shear displacements were a few centimetres at the proposed nuclear waste repository level, at proximately 500 m b.s.l. High-resolution, low-frequency echo-sounding was used to examine the Holocene submarine sedimentary structures and possible direct and indirect indicators of palaeoseismic activity in the northern Baltic Sea. Echo-sounding profiles of Holocene submarine sediments revealed slides and slumps, normal faults, debris flows and turbidite-type structures. The profiles also showed pockmarks and other structures related to gas or groundwater seepages, which might be related to fracture zone activation. Evidence of postglacial reactivation in the study area was derived from the spatial occurrence of some of the structures, especial the faults and the seepages, in the vicinity of some old bedrock fracture zones. Palaeoseismic event(s) (a single or several events) in the Olkiluoto area were dated and the palaeoenvironment was characterized using palaeomagnetic, biostratigraphical and lithostratigraphical methods, enhancing the reliability of the chronology. Combined lithostratigraphy, biostratigraphy and palaeomagnetic stratigraphy revealed an age estimation of 10 650 to 10 200 cal. years BP for the palaeoseismic event(s). All Holocene sediment faults in the northern Baltic Sea occur at the same stratigraphical level, the age of which is estimated at 10 700 cal. years BP (9500 radiocarbon years BP). Their movement is suggested to have been triggered by palaeoseismic event(s) when the Late Weichselian ice sheet was retreating from the site and bedrock stresses were released along the bedrock fracture zones. Since no younger or repeated traces of seismic events were found, it corroborates the suggestion that the major seismic activity occurred within a short time during and after the last deglaciation. The origin of the gas/groundwater seepages remains unclear. Their reflections in the echo-sounding profiles imply that part of the gas is derived from the organic-bearing Litorina and modern gyttja clays. However, at least some of the gas is derived from the bedrock. Additional information could be gained by pore water analysis from the pockmarks. Information on postglacial fault activation and possible gas and/or fluid discharges under high hydraulic heads has relevance in evaluating the safety assessment of a planned spent nuclear fuel repository in the region.

The role of lakes in carbon cycling in boreal catchments

Lakes are an important component of ecosystem carbon cycle through both organic carbon sequestration and carbon dioxide and methane emissions, although they cover only a small fraction of the Earth's surface area. Lake sediments are considered to be one of rather perma-nent sinks of carbon in boreal regions and furthermore, freshwater ecosystems process large amounts of carbon originating from terrestrial sources. These carbon fluxes are highly uncer-tain especially in the changing climate. -- The present study provides a large-scale view on carbon sources and fluxes in boreal lakes situated in different landscapes. We present carbon concentrations in water, pools in lake se-diments, and carbon gas (CO2 and CH4) fluxes from lakes. The study is based on spatially extensive and randomly selected Nordic Lake Survey (NLS) database with 874 lakes. The large database allows the identification of the various factors (lake size, climate, and catchment land use) determining lake water carbon concentrations, pools and gas fluxes in different types of lakes along a latitudinal gradient from 60oN to 69oN. Lakes in different landscapes vary in their carbon quantity and quality. Carbon (C) content (total organic and inorganic carbon) in lakes is highest in agriculture and peatland dominated areas. In peatland rich areas organic carbon dominated in lakes but in agricultural areas both organic and inorganic C concentrations were high. Total inorganic carbon in the lake water was strongly dependent on the bedrock and soil quality in the catchment, especially in areas where human influence in the catchment is low. In inhabited areas both agriculture and habitation in the catchment increase lake TIC concentrations, since in the disturbed soils both weathering and leaching are presumably more efficient than in pristine areas. TOC concentrations in lakes were related to either catchment sources, mainly peatlands, or to retention in the upper watercourses. Retention as a regulator of the TOC concentrations dominated in southern Finland, whereas the peatland sources were important in northern Finland. The homogeneous land use in the north and the restricted catchment sources of TOC contribute to the close relationship between peatlands and the TOC concentrations in the northern lakes. In southern Finland the more favorable climate for degradation and the multiple sources of TOC in the mixed land use highlight the importance of retention. Carbon processing was intensive in the small lakes. Both CO2 emission and the Holocene C pool in sediments per square meter of the lake area were highest in the smallest lakes. How-ever, because the total area of the small lakes on the areal level is limited, the large lakes are important units in C processing in the landscape. Both CO2 and CH4 concentrations and emissions were high in eutrophic lakes. High availability of nutrients and the fresh organic matter enhance degradation in these lakes. Eutrophic lakes are often small and shallow, enabling high contact between the water column and the sediment. At the landscape level, the lakes in agricultural areas are often eutrophic due to fertile soils and fertilization of the catchments, and therefore they also showed the highest CO2 and CH4 concentrations. Export from the catchments and in-lake degradation were suggested to be equally important sources of CO2 and CH4 in fall when the lake water column was intensively mixed and the transport of sub-stances from the catchment was high due to the rainy season. In the stagnant periods, especially in the winter, in-lake degradation as a gas source was highlighted due to minimal mixing and limited transport of C from the catchment. The strong relationship between the annual CO2 level of lakes and the annual precipitation suggests that climate change can have a major impact on C cycling in the catchments. Increase in precipitation enhances DOC export from the catchments and leads to increasing greenhouse gas emissions from lakes. The total annual CO2 emission from Finnish lakes was estimated to be 1400 Gg C a-1. The total lake sediment C pool in Finland was estimated to be 0.62 Pg, giving an annual sink in Finnish lakes of 65 Gg C a-1.

The prehistory of Suomussalmi, eastern Finland; the first billion years as revealed by isotopes and the composition of granitoid suites

The four papers summarized in this thesis deal with the Archean and earliest Paleoproterozoic granitoid suites observed in the Suomussalmi district, eastern Finland. Geologically, the area belongs to the Kianta Complex of the Western Karelian Terrane in the Karelian Province of the Fennoscandian shield. The inherited zircons up to 3440 Ma old together with Sm Nd and Pb Pb data confirm the existence of previously anticipated Paleoarchean protocrust in Suomussalmi. The general timeline of granitoid magmatism is similar to that of the surrounding areas. TTG magmatism occurred in three distinct phases: ca 2.95 Ga, 2.83 2.78 Ga and 2.76 2.74 Ga. In Suomussalmi the TTGs sensu stricto (K2O/Na2O less than 0.5) belong to the low-HREE type and are interpreted as partial melts of garnet amphibolites, which did not significantly interact with mantle peridotites. Transitional TTGs (K2O/Na2O more than 0.5), present in Suomussalmi and absent from surrounding areas, display higher LILE concentrations, but otherwise closely resemble the TTGs sensu stricto and indicate that recycling of felsic crust commenced in Suomussalmi 200 Ma earlier than in surrounding areas. The youngest TTG phase was coeval with the intrusion of the Likamännikkö quartz alkali feldspar syenite (2741 ± 2 Ma) complex. The complex contains angular fragments of ultrabasic rock, which display considerable compositional heterogeneity and are interpreted as cumulates containing clinopyroxene (generally altered to actinolite), apatite, allanite, epidote, and albite. The quartz alkali feldspar syenite cannot be regarded as alkaline sensu stricto, despite clear alkaline affinities. Within Likamännikkö there are also calcite carbonatite patches, which display mantle-like O- and C-isotope values, as well as trace element characteristics consistent with a magmatic origin, and could thus be among the oldest known carbonatites in the world. Sanukitoid (2.73 2.71 Ga) and quartz diorite suites (2.70 Ga) overlap within error margins and display compositional similarities, but can be differentiated from each other on the basis of higher Ba, K2O and LREE contents of the sanukitoids. The Likamännikkö complex, sanukitoids and quartz diorites are interpreted as originating from the metasomatized mantle and mark the diversification of the granitoid clan after 200 Ma of evolution dominated by the TTG suite. Widespread migmatization and the intrusion of anatectic leucogranitoids as dykes and intrusions of varying size took place at 2.70 2.69 Ga, following collisional thickening of the crust. The leucogranitoids and leucosomes of migmatized TTGs are compositionally alike and characterized by high silica contents and a leucocratic appearance. Due to compositional overlap, definitive discrimination between leucogranitoids and transitional TTGs requires isotope datings and/or knowledge of field relationships. Leucogranitoids represent partial melts of the local TTGs, both the sensu stricto and transitional types, mostly derived under water fluxed conditions, with possible fluid sources being late sanukitoids and quartz diorites as well as dehydrating lower crust. The Paleoproterozoic 2.44 2.39 Ga A-type granitoids of the Kianta Complex emplaced in an extensional environment are linked to the coeval and more widespread mafic intrusions and dykes observed over most of the Archean nucleus of the Fennoscandian shield. The A-type intrusions in the Suomussalmi area are interpreted as partial melts of the Archean lower crust and display differences in composition and magnetite content, which indicate differences in the composition and oxidation state of the source.

Neoarchean sanukitoid series in the Karelian Province, Finland

Sanukitoid series intrusions can be found throughout the Archean Karelian Province of the Fennoscandian shield. All sanukitoids share the same controversial elemental characteristics: they have high content of incompatible elements such as K, Ba, and Sr as well as high content of the compatible elements Mg, Cr, and Ni, and high Mg#. This composition is explained by an enriched mantle wedge origin in a Neoarchean subduction setting. This study concentrates on sanukitoid intrusions and tonalite-trondhjemite-granodiorite series (TTGs) from Finnish part of the Karelian Province. The collected rock samples have been studied in the field and under microscope as well as for their whole-rock (including isotopes) and mineral compositions. The new data together with previously published analyses help us to better understand the petrogenesis, tectonic setting and reworking of the Archean rock units. TTGs from the Karelian Province form a voluminous series of granitoids and reworked migmatites. This study divides TTG series into two subgroups based on their elemental composition: low-HREE (heavy rare earth element) TTGs and high-HREE TTGs indicating pressure differences in their source. Sanukitoid series is a minor, divergent group of intrusions. These intrusions are variable sized, and the texture varies from even-grained to K-feldspar porphyritic. The elemental composition differentiates sanukitoids from more voluminous TTG groups, the SiO2 in sanukitoids varies to include series of gabbro, diorite, and granodiorite. U Pb age determinations from sanukitoid series show temporally limited emplacement between ~ 2745 2715 Ma after the main crust forming period in the area. Hafnium, neodymium, common lead, and oxygene isotopes indicate well homogenized characteristics. Recycled crust has made a variable, yet minor, contribution to sanukitoids, as evidenced by oxygene isotopes and inherited zircon cores. A proposed tectonic setting for the formation of the sanukitoid series is slab breakoff of oceanic lithosphere in subduction setting, with sanukitoids deriving from an enriched mantle wedge. The proposed setting explains some of the peculiar features of sanukitoids, such as their temporally limited occurrence and controversial elemental composition. Sanukitoids would occur after cessation of the regional growth of Archean crust, and they could be derived from mantle wedge previously enriched by melts and fluids from oceanic crust and sediments. A subsequent event during the Paleoproterozoic Svecofennian orogeny at ~1.9 Ga affected the appearance and microstructures of the rocks as well as caused redistribution of lead between minerals and whole rock. However, the deformation was not able to obliterate the original geochemical characteristics of these sanukitoids.

Valtatie 21 Kolari - Kilpisjärvi : Toimenpideselvitys

Tehtävänä oli laatia toimenpideselvitys valtatielle 21 välille Kolari - Kilpisjärvi. Noin 280 kilometrin mittainen tarkastelujakso sijoittuu Suomi-neidon käsivarteen Kolarin, Muonion ja Enontekiön kuntien alueelle. Valtatie 21 osana kansainvälistä E8 -tietä on Pohjois-Kalotin ja Länsi-Lapin merkittävin pohjois-etelä -suuntainen pääväylä, jolla on suuri merkitys alueen väestölle, elinkeinoelämälle ja matkailulle. Tie palvelee nykyään erityisesti kalottialueen kuljetuksia Tromssan ja Finnmarkin talousalueille sekä Norjan kalateollisuuden kuljetuksia, jotka ovat voimakkaasti kasvavassa roolissa tien käyttäjinä. Tarkasteluvälille on ominaista valtatien kapeus ja laatutason voimakas vaihtelu. Nykyinen tie ei vastaa leveydeltään, geometrialtaan tai kunnoltaan valtatielle asetettuja minimivaatimuksia. Ajo-olosuhteet ovat erityistä tarkkaavaisuutta vaativat, talviaikaan jopa erittäin vaativat. Keskimääräinen vuorokausiliikennemäärä vaihtelee tarkasteluvälillä 350 - 1500 ajon./vrk, josta raskaan liikenteen osuus on 13 - 20 %. Liikenteen kausivaihtelu on erittäin suurta. Viikkokausivaihtelukäyrissä erottuvat selvästi hiihto-, pääsiäis- ja kesälomat sekä ruska-aika. Vuosina 2005- 2014 tarkastelujaksolla tapahtui yhteensä 121 poliisin tietoon tullutta onnettomuutta, joista 60 % johti henkilövahinkoihin. Tarkastelujakson henkilövahinko-onnettomuusaste on varsin korkea ja ylittää valtakunnallisen ja Lapin valtateiden keskiarvon selvästi. Rekkojen tieltä suistumisia tapahtuu talvikaudella paljon. Porokolarit ovat yleisiä. Tarkasteluosuudella valtatie 21 sijoittuu kolmelle metsäkasvillisuusvyöhykkeelle, joten luonnonympäristön ominaisuudet muuttuvat voimakkaasti etelä-pohjois-suunnassa. Käsivarren alueen ilmasto ja kallioperä poikkeaa muusta Pohjois-Lapista. Valtatien ympäristössä on pohjoiselle Lapille tyypillisesti aapasoita ja niiden paikallisia muunnoksia palsasoita, joiden jääsydän säilyy sulamatta yli kesän. Suunnittelualueella on runsaasti luontoarvoja ja laajaalaisia luonnonsuojelualueita. Laajimmat suojelualueet koostuvat erämaa-alueista ja luonnonpuistoista. Alueella on myös paljon soidensuojelualueita. Selvitysalueen koko vesistöalue on Natura 2000 -aluetta lukuun ottamatta kolmen laskujoen vesistöaluetta. Tunturi-Lapin alueella on runsaasti pohjavesialueita, joita valtatie 21 risteää useassa kohtaa. Valtatien tuntumassa on useita sekä valtakunnallisesti arvokkaita että maakunnallisesti arvokkaita maiseman ja kulttuuriperinnön kohteita. Suuri osa näistä kohteista on pieniä pistemäisiä kohteita. Valtatien 21 kehittämiselle asetettiin tavoitetila vuodelle 2045. Tällöin valtatie on kotimaisen ja kansainvälisen liikenteen pääkulkuväylä seudulla ja osa korkealuokkaista Eurooppatie-verkostoa. Liikenne on sujuvaa ja liikkuminen on turvallista kaikilla liikkumismuodoilla ja kaikkina vuodenaikoina. Tien leveys, geometria ja rakenne on kunnostettu ja kohtaamistilanteet ovat turvallisia. Matka-ajat ovat kohtuulliset ja hyvin ennakoitavissa. Olosuhteista ja häiriötilanteista tiedotetaan reaaliajassa. Taajamissa liikkuminen on turvallista kaikilla kulkumuodoilla. Valtatie 21 tunnetaan nykyistä paremmin Revontultentienä, joka tarjoaa laadukkaan matkailutie-elämyksen palveluineen matkailijoille. Valtatie 21 esitetään Kolarin ja Kilpisjärven välillä parannettavaksi suurelta osin nykyisellä paikallaan. Tie ja sillat levennetään ja tien rakennetta vahvistetaan tai rakenne uusitaan käytännössä lähes koko matkalla aiemmin rakennettuja taajamakohtia lukuun ottamatta. Kokonaan uutta tietä tehdään Muotkatakka-Kilpisjärvi -välillä nykyisen tien viereen rakentaen. Kinostumista ehkäistään loiventamalla luiskia, jolloin ei muodostu kinostavaa taitetta. Ongelmaiset palsasuokohteet rakennetaan niin, etteivät routavauriot uusiudu. Taajamissa toimenpiteinä ovat turvallisten tien ylityspaikkojen rakentaminen huolella valittuihin kohteisiin ja systemaattinen ajonopeuksien hillintä. Taukopaikkoja rakennetaan lisää ja nykyisiä kunnostetaan. Tieympäristö kohennetaan raivaamalla umpeen kasvaneita kohtia tien varressa ja avaamalla tiellä kulkijalle jokinäkymiä. Taukopaikkojen ympäristöt raivataan ja siistitään. Poronhoidon ja liikenteen ristiriitoja vähennetään mm. ottamalla käyttöön digitaalinen porovaroitusjärjestelmä.