Browsing by Subject "FENNOSCANDIAN SHIELD"

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  • Purkamo, Lotta; Bomberg, Malin; Kietäväinen, Riikka; Salavirta, Heikki; Nyyssonen, Mari; Nuppunen-Puputti, Maija; Ahonen, Lasse; Kukkonen, Ilmo; Itavaara, Merja (2016)
    The bacterial and archaeal community composition and the possible carbon assimilation processes and energy sources of microbial communities in oligotrophic, deep, crystalline bedrock fractures is yet to be resolved. In this study, intrinsic microbial communities from groundwater of six fracture zones from 180 to 2300aEuro-m depths in Outokumpu bedrock were characterized using high-throughput amplicon sequencing and metagenomic prediction. Comamonadaceae-, Anaerobrancaceae- and Pseudomonadaceae-related operational taxonomic units (OTUs) form the core community in deep crystalline bedrock fractures in Outokumpu. Archaeal communities were mainly composed of Methanobacteriaceae-affiliating OTUs. The predicted bacterial metagenomes showed that pathways involved in fatty acid and amino sugar metabolism were common. In addition, relative abundance of genes coding the enzymes of autotrophic carbon fixation pathways in predicted metagenomes was low. This indicates that heterotrophic carbon assimilation is more important for microbial communities of the fracture zones. Network analysis based on co-occurrence of OTUs revealed possible "keystone" genera of the microbial communities belonging to Burkholderiales and Clostridiales. Bacterial communities in fractures resemble those found in oligotrophic, hydrogen-enriched environments. Serpentinization reactions of ophiolitic rocks in Outokumpu assemblage may provide a source of energy and organic carbon compounds for the microbial communities in the fractures. Sulfate reducers and methanogens form a minority of the total microbial communities, but OTUs forming these minor groups are similar to those found in other deep Precambrian terrestrial bedrock environments.
  • Gong, Zheng; Evans, David A. D.; Elming, Sten-Åke; Söderlund, Ulf; Salminen, Johanna M. (2018)
  • Purkamo, Lotta; Bomberg, Malin; Nyyssönen, Mari; Ahonen, Lasse; Kukkonen, Ilmo; Itävaara, Merja (2017)
    Acetate plays a key role as electron donor and acceptor and serves as carbon source in oligotrophic deep subsurface environments. It can be produced from inorganic carbon by acetogenic microbes or through breakdown of more complex organic matter. Acetate is an important molecule for sulfate reducers that are substantially present in several deep bedrock environments. Aceticlastic methanogens use acetate as an electron donor and/or a carbon source. The goal of this study was to shed light on carbon cycling and competition in microbial communities in fracture fluids of Finnish crystalline bedrock groundwater system. Fracture fluid was anaerobically collected from a fracture zone at 967 m depth of the Outokumpu Deep Drill Hole and amended with acetate, acetate + sulfate, sulfate only or left unamended as a control and incubated up to 68 days. The headspace atmosphere of microcosms consisted of 80% hydrogen and 20% CO2. We studied the changes in the microbial communities with community fingerprinting technique as well as high-throughput 16S rRNA gene amplicon sequencing. The amended microcosms hosted more diverse bacterial communities compared to the intrinsic fracture zone community and the control treatment without amendments. The majority of the bacterial populations enriched with acetate belonged to clostridial hydrogenotrophic thiosulfate reducers and Alphaproteobacteria affiliating with groups earlier found from subsurface and groundwater environments. We detected a slight increase in the number of sulfate reducers after the 68 days of incubation. The microbial community changed significantly during the experiment, but increase in specifically acetate-cycling microbial groups was not observed.
  • Luoto, Toni; Salminen, Johanna; Obst, Karsten (2021)
    Baltica and Laurentia form the core of the hypothesized Mesoproterozoic supercontinent Nuna in most paleogeographical reconstructions. Long gaps still exist in the Mesoproterozoic paleomagnetic record of Baltica, and different relative configurations for Baltica and Laurentia have been presented. This study presents new paleomagnetic data obtained for mafic dykes on Bornholm (Denmark, southwest Baltica). We provide a new 1.326 +/- 0.010 Ga Bornholm Group I paleomagnetic key pole (Plat: 06 degrees N, Plon: 165 degrees E, K: 21, A95: 6 degrees) for Baltica. This pole supports the low-latitude equatorial core of Nuna at 1.33 Ga, where Kola Peninsula and Northern Norway of Baltica were facing northeastern Greenland of Laurentia. Based on statistically different magnetization directions with Group I and differences in Nb-Zr-Y systematics, we propose a separate Bornholm Group II paleomagnetic pole. This undated, poor-quality pole indicates a paleolatitude of ca. 50 degrees, possibly reflecting an age difference compared to Group I, accompanied with the continental drift. On Bornholm, the wide Listed and Kas dykes of uncertain age yield significantly different paleomagnetic results compared to the other studied dykes there. In addition, the virtual geomagnetic poles (VGPs) of these dykes are 45 degrees apart from each other. On the basis of similar Nb-Zr-Y systematics with the dykes of the 0.98-0.94 Ga Blekinge Dalarna Dolerite Group (Sweden) and overlapping paleomagnetic data with the high-quality 0.95-0.94 Ga paleomagnetic poles of Baltica, an early Neoproterozoic age for the magnetization is proposed. The relatively big discrepancy between Listed and Kas VGPs could stem from an unaveraged paleosecular variation or from a small but significant age difference during rapid plate movements.
  • Chopin, Francis; Korja, Annakaisa; Nikkila, Kaisa; Holtta, Pentti; Korja, Toivo; Zaher, Mohamed Abdel; Kurhila, Matti; Eklund, Olav; Ramo, Tapani (2020)
    Tectonic evolution of the Paleoproterozoic Vaasa migmatitic complex (VMC) in the central part of the Svecofennian accretionary orogen is deciphered using aeromagnetic and gravity maps, deep seismic and magnetotelluric profiles, and structural and metamorphic data. The VMC is a semicircular structure with migmatitic rim and granitic core composed of several subdomes. It evolved in three main tectonic events (D1-D3). The D1 event (ca. 1.89-1.88 Ga) corresponds to the stacking of supracrustal rocks and the formation of an inverted metamorphic gradient. Anatexis at LP-HT metamorphic conditions enabled the material to flow. The D2 event (ca. 1.88-1.87 Ga) corresponds to large-scale folding of the partially molten crust within an orocline. It is marked by folds with an E-W vertical axial planar foliation. The late D3 event resulted from mass redistribution owing to mechanical instabilities within the hinge of the orocline. It is marked by vertical shearing (ca. 1.87-1.85 Ga) in the marginal parts of the complex and along the granitoid subdomes. The seismic reflection profile (FIRE 3a) and magnetotelluric profiles (MT-PE and MT-B2) image large-scale D1 stacking structures within an accretionary prism. Near vertical breaks in crustal-scale reflectivity and conductivity models are interpreted as D3 shear zones. The VMC is an example of early mass and heat transfer within a collage of hot supracrustal rocks in an accretionary belt. Partial melting enhanced the flow of material, the production, and rise of magma as well as exhumation, marked by magmatic domes in the hinge of the orocline.