Browsing by master's degree program "Geologian ja geofysiikan maisteriohjelma"

Continental flood basalts (CFBs) in the Karoo large igneous province were formed 189–178 Ma ago during the breakup of the Gondwana supercontinent. The flood basalts are found in the southern part of Africa, in Antarctica, and in the Falkland. The Karoo province can be divided into the North Karoo and South Karoo subprovinces on the basis of the geochemical compositions of the CFBs. The source of the South Karoo lavas has been interpreted to consist of pyroxenitic mantle and depleted upper mantle. The North Karoo lavas have been less well studied. The source of the North Karoo lavas at Luenha River, Mozambique, has been interpreted to be in a primitive part of the African LLSVP (Large Low Shear Velocity Province) in deep mantle. It is also believed that they have surfaced as part of a mantle plume. The results on the mantle source of the North Karoo CFBs have not been conclusive, however. In this study I analyze olivine crystals from the Luenha River picrites and utilize their mineral composition to address the mantle source of the North Karoo lavas. Four of the samples from Luenha River contain fresh olivine. They were analyzed using EPMA. All the analyzed olivine crystals are within Fo77–89. The compositional variation within the samples is relatively small and there is no evidence of multiple olivine populations. The olivine compositions support the proposed primitive peridotitic mantle source of the Luenha picrites. They are very similar to the olivines of the Etendeka CFBs that have been interpreted to be from peridotitic mantle source. The olivines from the Luenha picrites have high Mn/Fe ratios and low Ni, Ca, and Zn concentrations, which indicates a peridotitic source. The portions of pyroxenite and recycled oceanic crust were calculated to be less than 10 weight percent. In two samples, the crystallization temperatures were determined to be 1207–1368°C using an Al-in-olivine thermometer. Combined use of the Al-in olivine and the melt-olivine Mg-Fe equilibrium thermometers enabled the estimation of the temperatures of the primary melts (Fo92). The temperatures of the primary melts were 1300–1472°C, which supports the theory of Luenha picrites being derived from a mantle plume.

Global warming and anthropogenic activity will change the environmental conditions in the northern regions. For example, precipitation and river flow are expected to increase, the amount of organic matter ending up in the sea from land will increase, and its quality will change. The impact of changes in organic matter on northern coastal ecosystems and the carbon cycle is poorly known and these impacts need to be studied. In this study, the amount, quality and variations of organic matter accumulated in the surface sediments of the Bothnian Bay coastal areas in the northern part of the Baltic Sea and in the Liminka Bay over the past 100 years are studied by analyzing the concentrations of organic carbon and nitrogen (TOC and TN), C/N ratio, and the stable isotope ratios δ13C and δ15N, thus assessing environmental change in the coastal area of the Bothnian Sea. The accumulation of organic matter along the coast of Bothnian Bay is affected by both the proximity of the rivers and the land cover and land use of the river basin. More organic matter accumulates on the coasts (average 3.5 wt%) than further into the open sea (average 1.9 wt%). Contrary to presuppositions, there is no clear variation in the quality of organic matter between the coast and the open sea, but the observed change is north-south: in the northern areas, organic matter is more terrestrial and autochthonous, and in the southern areas it is more aquatic and allochthonous. The northern regions are characterized by large rivers with large amounts of forests and peatlands in the catchment areas. Further south, the rivers are smaller and carry less organic matter in quantity. Further north in the coastal ecosystem, the amount of primary production is lower and nitrogen does not limit primary production, as opposed to more southern areas. Primary production of ice may also have affected the organic matter deposited in the Bothnian Sea sediments. The amount of organic matter deposited in Liminka Bay has been on the rise over the past century, probably due to global warming, increased river flow and the impact of human activity. Based on the C/N ratio, the material has been more terrestrial in the 1930s to 1970s, after which the material has become more aquatic. In addition, aquatic primary production has increased in the Liminka Bay and nitrogen has begun to restrict primary production more. The study shows that climate and environmental change and human activities affect the amount and quality of organic matter in northern coastal areas, but further research is needed to determine more accurate ecosystem impacts.

The Bjurböle meteorite, which fell near Porvoo in 1899, is categorised as a fall. The Bjurböle meteorite is classified as an L/LL4 ordinary chondrite. Chondrites are undifferentiated meteorites that contain notable amounts of non-volatile elements of the early solar system. Chondrites usually contain small spherical igneous chondrules and they are classified into three groups: carbonaceous (C), enstatite (E) and ordinary chondrites (O). Ordinary chondrites are further classified into groups H, L and LL according to their metallic iron content. Chondrites are classified into petrologic types 1 – 6 based on their metamorphic grade so that Type 3 is the least metamorphosed and Type 6 is the most strongly metamorphosed, whereas Type 1 and Type 2, on the other hand correspond to meteorites that are, respectively, strongly and mildly affected by low-temperature aqueous alteration processes. The chemical equilibration of chondrites is controlled by the degree of metamorphism they go through. The more equilibrated a chondrite is, the more simplified its mineral assemble is and the more homogenised compositions the minerals have. Chondrules contain mostly olivine, pyroxene and interchondrule matrix. They are classified into Type I and Type II by the compositions of their olivine and pyroxene. Chondrule types can be further divided into A, B and AB by their olivine content. In addition, chondrules can be classified according to their texture into porphyritic, barred, radial, granular, cryptocrystalline, and metallic chondrules. The aim of this thesis is to inspect the variation in olivine composition in Bjurböle meteorite chondrules, to document the petrography of the Bjurböle meteorite and to find connections between petrographic discoveries and olivine composition. Furthermore, in this study I will discuss about the classification of the Bjurböle meteorite and the formation of chondrules in the Bjurböle meteorite. For this study, I examined 11 thin sections and three epoxy buttons that have 34 chondrules in total. Thin sections were inspected by microscope and six of the uncoated thin sections were also inspected under cold-cathode luminescence. The epoxy buttons were inspected with a scanning electron microscope, scanning electron microscope cathodoluminescence and scanning electron microscope energy-dispersive X-ray spectroscopy. Most of the inspected chondrules in the Bjurböle meteorite samples have very uniform olivine composition, as reported in earlier studies. Most of the olivines are Fo75–78, but there is also a bimodal peak at Fo89–92. The E1 chondrules (small) have very uniform olivine compositions of approximately Fo76–77. The E2 chondrules (medium) have also olivines of approximately Fo76–77, but some of the olivines reach Fo80–83. The E3 chondrules (large) have the broadest olivine composition variation at Fo74–93. However, most of the E3 olivines are Fo76–79. The E3-2 chondrule, in particular, has a broad olivine composition variation and its Fo-value increases up to 93 in the core of the chondrule. All chondrules with broader olivine variation have barred texture and are relatively large. Cathodoluminescence did not provide substantial data for the study. Other links between olivine compositions and petrography were not observed and, for example, proximity to metallic phases did not seem to have any effect on the olivine composition, and the exceptionally Mg-rich (Fo90) olivines may represent primary compositions. E3-6 and E3-7 chondrules are abundant in sulphide and metallic phases. The E3-7 chondrule resembles something that might be called micropallasite. Based on porosity, magnetic susceptibility, metamorphic signs, and the Fe variation in olivine and mineral assemblages, the Bjurböle meteorite fits the classification of an L/LL4 ordinary chondrite. Chondrules of the Bjurböle meteorite also have diverse forming histories.

Archean cratons hold information of the early crustal development of the Earth, in conditions much different than the ones that exist today. Archean cratons consist of felsic plutonic rocks and greenstone belts. These belts are a useful tool for the understanding of the development of the early geological processes that shaped the Earth. There has been a variety of suggestions regarding the origin and geodynamic conditions that formed the Archean greenstone belts and there are several possible geotectonic scenarios that could form them. This thesis focuses on the Takanen greenstone belt found in the Karelia province in the Fennoscandian shield. The main objective of this study is to constrain the age of the greenstone belt, as well as to classify and group the formations found in it and compare it with its neighbouring, and much larger, Suomussalmi-Kuhmo-Tipasjärvi greenstone belt system - the biggest complex of its kind in the Karelian craton. A diamond drilling profile across the Takanen belt has been sampled. The various rocks found in the belt are divided into 5 groups based on their thin-section petrography and major and trace element geochemistry, outlining the general stratigraphy of the belt. There are also whole rock analyses that help to obtain major and trace element geochemical data for multiple samples from different locations throughout the belt. There are 3 calc-alkaline units (CALC1, CALC2, CALC3, named after their predominantly calc-alkaline nature) that include felsic, to intermediate volcanic/volcanosedimentary rocks and 2 units that consist of channelized komatiitic lavas and tholeiitic basalts (KOMBAS, named after the komatiites and basalts of the unit), olivine/olivine-pyroxene cumulates and high-Mg to tholeiitic basalts (OLIAD, named after the abundance of olivine adcumulates). The CALC1 unit is found lowest in the stratigraphy of the area and bares the oldest age of 2.95 Ga, while CALC3, which is the youngest formation of the belt, gives an age of 2.7 Ga. There is a direct correlation with the lowest CALC1 unit and the Luoma group in the Suomussalmi greenstone belt in terms of petrography, geochemistry and age, indicating that Takanen is the continuation of the Suomussalmi-Kuhmo-Tipasjärvi system to the north. Based on the initial Lu-Hf isotope composition of the dated samples, and the stratigraphic layering of Takanen, the oldest units in the belt originate from a process of continental rifting, while the youngest ones were most likely formed by a combination of continental rifting and some interaction of the continental crust with oceanic lithosphere. The Takanen greenstone belt lies on top of a large positive gravimetric and magnetic anomaly in the Koillismaa area called the ‘‘hidden dyke’’, composed of mafic-ultramafic cumulates and hypothesized to be related to the Paleoproterozoic Koillismaa-Näränkävaara Layered Intrusion Complex. The dyke and Takanen may not be genetically related, yet their overlapping existence points to a large crustal structure that served as a magma pathway throughout the Archean and the Paleoproterozoic. The potential of an economic orthomagmatic nickel deposit related to Takanen should not be completely overlooked, as there are some favorable indications in the geochemistry of the komatiitic units, as well as their possible interaction of these units with older sulphur rich units of the belt.

A NW–SE trending dike swarm cuts Miocene volcanic rocks in the Ibex Hills and Precambrian to Cambrian cratonic rocks and sedimentary strata in the Saddlepeak Hills and Salt Spring Hills in southern Death Valley, California. These dikes are aligned with Jurassic and Cretaceous dike swarms of eastern California that are linked to the Mesozoic North American Cordilleran magmatism. The Ibex Hills dikes have been previously dated and yield K-Ar date of 12.7 Ma and are coeval with the early stage of the Miocene Basin and Range crustal extension in Death Valley. This Master’s thesis examines in detail the geology, petrography and geochemistry of the previously unstudied dikes of Ibex Hills, Saddlepeak Hills and Salt Spring Hills of southern Death Valley and a ~90 Ma dike of Mojave Desert to discuss (1) their petrogenetic link to each other and (2) their geologic significance. The samples and field observations were obtained in 2019. The Ibex Hills samples are relatively fresh compared to the dikes of Saddlepeak Hills and Salt Spring Hills which are pervasively altered by secondary minerals and have been subject to low-grade metamorphism. The sub-solidus processes that have modified the mineral assemblages of the metamorphic dikes are also reflected in various degrees of major element mobility and LOI. The whole-rock geochemical composition of the Ibex Hills and Mojave Desert samples is trachyandesite to trachyte, the Saddlepeak Hills and Salt Spring Hills samples are andesites. One Saddlepeak Hills sample is basaltic and, based on mineralogy, texture and composition, represents a 1.1 Ga diabase intrusion. All studied samples are enriched in LREEs and LILEs and have negative Ta-Nb anomaly, representing magmas with typical subduction zone characteristics with enriched lithospheric mantle component in source. EPMA and in situ LA-MC-ICP-MS analysis of plagioclase phenocrysts of two Miocene samples of Ibex Hills shows variation in anorthite content and 87Sr/86Sr ratios across phenocryst profiles indicating open-system magma chamber evolution with episodes of recharge, hybridization and assimilation during the crystallization. Variation in anorthite content and 87Sr/86Sr ratios between samples suggest heterogeneities in the source magmas. The studied dikes represent multiple episodes of dike emplacements in southern Death Valley. The Miocene dikes of Ibex Hills, coeval with the Basin and Range crustal extension, indicate an early period of southwest directed extension in the southern Death Valley. The metamorphosed dikes of Saddlepeak Hills and Salt Spring Hills represent one or more episodes of older dike emplacement and could be coeval with the Mesozoic magmatism of North American Cordilleran orogeny and the Cretaceous dike of Mojave Desert. However, geochronological analysis is needed to verify the exact ages of these dikes.

The aim of this study was to research surface water-groundwater interactions and groundwater flow directions with stable isotopes of water, dissolved silica, d-excess, electrical conductivity, pH and temperature in the Vesioronkangas groundwater area in the city of Imatra, South-Carelia. Elevations of groundwater pipe heads existing in year 2015 were measured and connected to N2000-elevation system, and their coordinates were checked. Groundwater levels were measured, and pipe coordinates checked in the summer of 2015. Water samples were collected in the late winter of 2016 and temperature, pH and electrical conductivity of the samples were determined on site with YSI multiparameter probe. The samples were analyzed in the University of Helsinki laboratory during the spring and summer of 2016. Stable isotopes δ18O and δD were analyzed with Picarro L1115-i device and dissolved silica with Agilent 4100 device. Electrical conductivity was measured again in the laboratory after heating the samples. In the cluster analysis, the water samples formed three groups that were already detectable on the basis of the stable isotope composition of the water and other physical and chemical variables: surface waters, groundwater-influenced surface waters/mixed waters and groundwaters. Maps and flow and structural modellings of the groundwater area were created with QGIS and TopoDrive programs and it seems that there is no hydraulic connection between Lake Saimaa and Lake Immalanjärvi even if there is a bedrock fracture zone. Groundwater flows to many directions in the area, almost all compass points.

The construction of the Savio railway tunnel caused an unexpectedly large decrease in the groundwater heads in part of the observation points in the vicinity of the railway tunnel after the completion of the tunnel construction work. The study aimed to investigate the ability of the groundwater model to forecast such groundwater drawdown caused by a railway tunnel in the urban areas of East Hakkila, Kaskela and Hakunila. The uncertainty of the groundwater model and its sensitivity to certain parameters were studied and analyzed. The groundwater model was built using the GMS (Groundwater Modeling System) numerical groundwater modeling program. For the groundwater flow model, the bedrock mesh was built in Leapfrog Geo - program based on gravimetric measurements and rotary drilling. The groundwater model was calibrated manually and automatically to correspond to the groundwater heads measured in the area. The circumstances after the construction of the railway tunnel were then simulated. The model-calculated groundwater heads were compared to the observed groundwater heads and the observed tunnel leakage. Sensitivity analysis was performed for the horizontal conductivity parameters and recharge parameters of the model. The groundwater model before the construction of the tunnel mimicked the measured groundwater heads and flow directions in the study area. The simulation of the time after the construction of the tunnel caused groundwater drawdown of 0-16 meters at 0-730 meters from the railway tunnel. In the simulation of the time after tunnel construction, the groundwater heads calculated by the model differed by 0,01-24 meters from measured groundwater heads. According to the results of the sensitivity analysis, the model was most sensitive to changes in the horizontal conductivity of the upper bedrock layer and granite. The recharge parameters and soil layer had a marginal impact on the groundwater model. The uncertainty of the model was affected by the few measurement points in relation to the size of the area and the absence of field measurements of the hydraulic conductivity of the parameters. To reduce the uncertainty, the model should be calibrated based on the measured conductivity values of the bedrock. Despite the uncertainty, computational models give indications of the direction of change and are important tools in questions related to nature and the built environment.

As a part of constructing the upcoming repository for spent nuclear fuel ONKALO®, Posiva Oy is investigating the hydrogeological structures of Olkiluoto bedrock. Posiva Flow Log (PFL) drillhole measurements are an important part in characterization of bedrock’s hydraulic properties. The measurements are conducted both from the surface and in the study site of ONKALO tunnel network. Results are used widely at the site from the planning of construction to the water conducting fracture characterization. PFL equipment are capable of measuring groundwater flow originating from a single fracture which enables small scale detection of transmissive fractures in bedrock. Equipment measures temperature variations in a water flow inside an isolated test section to determine the flow rate. Several other equipment for groundwater flow measurement are introduced to highlight the accuracy of PFL. Fractures measured with PFL DIFF were 3D modelled in twelve ONKALO pilot holes (ONK-PH13-20, ONK-PH23, ONK-PH26 and ONK-PH28-29) using FracMan software suitable for fracture network modelling. 3D model described the fracture locations with fracture orientation and pilot hole transmissive fracture traces projected to tunnel walls. Brittle fault zone intersection between the chosen pilot holes were also modelled. Three of the pilot holes (ONK-PH23, ONK-PH28 and ONK-PH29) were selected for the fracture correlation. Pilot hole transmissive fractures were connected with tunnel wall water leaking fractures located with systematic mapping and water leakage mapping. Criteria for connecting the fractures were fracture location, water leakage and fracture orientation. Structure intersections with brittle fault zones were studied individually for each pilot hole. 433 meters of ONKALO tunnels were included in the correlation with total 20 of pilot hole transmissive fractures and 18 tunnel wall water leaking fractures according to systematic mapping. 100 % of ONK-PH23, 75 % of ONK-PH28 and 16,7 % of ONK-PH29 pilot hole transmissive fractures were correlated with tunnel wall water leakages in the corresponding depths. Counterparts were found for nine fractures of total 20 studied fractures based on the listed attributes. Fracture correlation was unsuccessful with 11 of the observed transmissive fractures. Study produced new data for the possible fracture correlations and hydraulic connections were produced in the pilot hole areas. Views and opinions described in this thesis are interpretation of the author and do not necessarily represent Posiva’s views.

Maatalouden ravinnekuormituksella on suuri vaikutus viljelysmaiden alapuolisten vesistöjen rehevöitymiseen ja veden laatuun. Kaksitasouomat on suunniteltu viljelysmaiden tulvavesien hallintaan, mutta ne myös vähentävät ravinteiden huuhtoutumista yläjuoksun valuma-alueilta, kun virran kuljettamat sedimentit kertyvät tulvatasanteille. Tulvatasanteet tarjoavat myös suotuisat olosuhteet liukoisen fosforin sorptiolle sekä saostumiselle. Sedimentin ja siihen liittyvää ravinteiden kertymistä tulvatasanteille seurattiin kolmelta toisistaan erottuvalta eteläsuomalaiselta kaksitasouomalta niiden keskinäisen dynamiikan tutkimiseen. Suomen ympäristökeskuksen Valumavesi projekti asensi 32 keräintä kaksitasouoman tulvatasanteille 2021 kesän ja syksyn aikana, jotka kerättiin vuoden 2022 kesällä ja niistä analysoitiin sedimenttikertymä, geokemiallinen koostumus, ravinnepitoisuudet sekä fosforin eri fraktiot. Sedimenttikertymä oli suurempaa viljellyillä kivennäismailla (2.5–6.4 kg m-2 a-1), kuin orgaanisilla viljelysmailla (0.2 kg m-2 a-1), mikä vaikutti merkittävästi tulvatasanteiden ravinnekertymään. Yhdellä tutkimusalueella tämä tarkoitti 3–4 % uoman kiintoaineksen määrästä (2.3–3.2 tonnin sedimenttikertymää) 250 m tulvatasanteelle 223 päivän aikana. Jos tulvatasanteen kasvillisuuden niitto olisi laajennettu koskemaan koko tulvatasannetta, olisi sedimentin pidätyskyky kasvanut 3.3–4.7 % uoman kiintoaineskuormasta. Sedimenttikertymän paikkakohtaiseen vaihteluun vaikuttivat pinnan topografia, tulvinnan laajuus, tulvimistiheys, uoman vakaus ja kasvillisuuden hoitomenetelmät. Tutkimusalueiden geokemiallisen koostumuksen vaihtelu selittyi enimmäkseen sedimenttien kivennäis- ja orgaanisen aineksen määrällä, joka juontui valuma-alueen maaperästä. Maaperästä riippumattomat mangaanipitoisuudet selittivät tutkimusalueiden paikallista horisontaalista vaihtelua sedimenttikeräin näytteissä ja vertikaalista vaihtelua aikaisempien tutkimuksien sedimenttiprofiileissa. Redox-herkän mangaanin ja fosforifraktioiden vaihtelu tapahtui usein samanaikaisesti, jota käytettiin fosforidynamiikan tutkimiseen. Rautasidonnainen fosfori oli merkittävin fosforifraktio viljellyillä mineraali ja orgaanisilla mailla. Kivennäismailla oli enemmän detritaalista apatiittia vähän rapautuneista Litorinanmeren aikaisista savikoista, kun taas orgaanisilla mailla oli enemmän fosforia kiinnittyneenä ei-redusoituviin metalleihin, jotka muodostuvat hapettomammissa olosuhteissa. Tulvatasanteille kertyneet sedimentit eivät olleet kyllästyneet fosforista, mutta se on mahdollista ravinnerikkaiden sedimenttien edelleen kertyessä, jolla voi olla vaikutusta kaksitasouoman kunnostusmenetelmiin tulevaisuudessa. Kaikki tutkitut kaksitasouomat pidättivät ravinnerikkaita sedimenttejä, jonka tulisi näkyä pienempänä ravinnekuormituksena alajuoksun vesistöissä.

A seismic reflection survey was carried out at the Hannukainen-Rautuvaara Iron (Fe), Copper (Cu), and Gold (Au) deposits as part of the HIRE (High Resolution Reflection Seismics for Ore Exploration, 2007-2010) project. The main discovery from this survey was a regional structure showing three reflective layers dipping to the southwest. The top of this package of reflectors is currently planned to be mined at Hannukainen. The deeper parts of this package may have potential continuation of the economically viable deposits seen at shallow depths. In this work, a target-specific, amplitude-preserving workflow for profiles E1 and V5 of the Hannukainen-Rautuvaara HIRE seismic data will be formulated and applied. Then seismic amplitude vs. offset (AVO) and attribute analyses will be used to analyse the reflective layers and identify potential areas of interest for further study. This is a burgeoning area of seismic research, AVO analysis is typically used in hydrocarbon exploration and has only been sparsely used in hard rock settings for mineral exploration. Attribute analysis is more common in hard rock environments, but still underutilised. The seismic reflection data were re-processed focusing on retaining the high-frequency content of the seismic signal, this is key for further analysis. The results of the AVO analysis consist of determining the AVO class of the responses seen across the CMPs of two selected AVO horizons. AVO product and Poisson’s ratio change across the horizons were calculated, and an area of interest was identified from the correlation of these parameters. Attribute analysis was done using the seismic attributes envelope, first derivative envelope, Hilbert Transform, relative impedance, phase, weighted instantaneous frequency and dip. The amplitude attributes (envelope, first derivative envelope, Hilbert Transform, relative impedance) were useful in determining the areas of the reflector package that showed the strongest amplitudes and selecting horizons on the uppermost reflector for AVO analysis. Phase and weighted instantaneous frequency helped determine the continuity of the reflector package which revealed a clear four-layer signature, differing form the earlier three-layer interpretation. The dip attribute showed vertical anomalies, some of which correlated with mapped faulting in the area. Detailed interpretation of the geophysical results requires better borehole coverage, and petrophysical work, to tie in the seismic data results to the alteration and mineralisation. With open pit mine planning ongoing in the study area, the identification of deep-seated mineral deposits will have direct impact on the planning of the mine and the future of exploration in Hannukainen-Rautuvaara.