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- Hallberg, Rolf O., et al.
(författare)
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Microbial Fossils in the 2.63 Ga Jeerinah Formation, Western Australia-Evidence of Microbial Oxidation
- 2018
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Ingår i: Geomicrobiology Journal. - : Informa UK Limited. - 0149-0451 .- 1521-0529. ; 35:4, s. 255-260
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Tidskriftsartikel (refereegranskat)abstract
- A diamond drill core from the upper part of the Jeerinah Formation (similar to 2.63 Ga), underlying the Hamersley Group, deposited at a time when the oxygen concentrations in the marine environment were extremely low, was examined for microbial fossils. The paper presents organo-mineral structures in the form of twisted stalks produced by bacteria being present in the laminated black carbonaceous shale sediments. These twisted stalks are organo-mineral structures produced by microaerophilic Fe(II)-oxidizing-type bacteria such as Gallionella and/or Mariprofundus that are active at very low-oxygen concentrations, thus providing evidence for oxygen being present in the marine environment at 2.63 Ga.
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| 5. |
- Karageorgis, Aristomenis P., et al.
(författare)
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Authigenic carbonate mineral formation in the Pagassitikos palaeolake during the latest Pleistocene, central Greece
- 2013
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Ingår i: Geo-Marine Letters. - : Springer Science and Business Media LLC. - 0276-0460 .- 1432-1157. ; 33:1, s. 13-29
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Tidskriftsartikel (refereegranskat)abstract
- The Pagassitikos Gulf in Greece is a semi-enclosed bay with a maximum depth of 102 m. According to the present-day bathymetric configuration and the sea level during the latest Pleistocene, the gulf would have been isolated from the open sea, forming a palaeolake since 32 cal. ka b.p. Sediment core B-4 was recovered from the deepest sector of the gulf and revealed evidence of a totally different depositional environment in the lowest part of the core: this contained light grey-coloured sediments, contrasting strongly with overlying olive grey muds. Multi-proxy analyses showed the predominance of carbonate minerals (aragonite, dolomite and calcite) and gypsum in the lowest part of the core. Carbonate mineral deposition can be attributed to autochthonous precipitation that took place in a saline palaeolake with high evaporation rates during the last glacial-early deglacial period; the lowest core sample to be AMS C-14 dated provided an age of 19.53 cal. ka b.p. The palaeolake was presumably reconnected to the open sea at 13.2 cal. ka b.p. during the last sea-level rise, marking the commencement of marine sedimentation characterised by the predominance of terrigenous aluminosilicates and fairly constant depositional conditions lasting up to the present day.
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- Nordell, Bo, et al.
(författare)
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Leaching of rock fractures : laboratory and field tests for borehole heat stores
- 1988
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this project has been to employ chemical leaching to achieve sufficient hydraulic contact through fissures in the rock to enable them to serve as part of the circulation system of a borehole in the heat store.^The trials were carried out both in the laboratory and in the field.^The results obtained in the field were investigated by means of hydraulic tests that allowed the hydraulic conductivity to be determined.^The results were not as expected, rather they were the opposite.^Fissures in the rock were sealed instead of being opened up, and the hydraulic conductivity decreased instead of increasing.^The explanation for this lies in the fact that the leaching liquid, a solution of NaOH, became saturated by dissolved minerals which were then precipitated elsewhere in the fracture system.^However, this undesired result may turn out to have a number of geological engineering applications, as there is normally a greater need to seal fissures in rock than to open them.
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| 7. |
- Nordell, Bo, et al.
(författare)
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Leaching of rock fractures : Laboratory and field tests for borehole heat stores
- 1989
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Ingår i: Tunnelling and Underground Space Technology. - : Elsevier BV. - 0886-7798 .- 1878-4364. ; 4:1, s. 99-107
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this research project was to increase the hydraulic conductivity of fractured rock by pumping a leaching fluid (NaOH) through rock fractures. A 16-week field test was carried out in a borehole heat store consisting of 19 vertical boreholes to a depth of 15 m in gneissic rock. The leaching process was studied simultaneously in a laboratory test where rock samples from core drillings of the test site were used. The hypothesis that NaOH-solution would leach and thereby widen the fractuers, was not fulfilled. On the contrary, the fractures were sealed as the leaching test went on. The explanation for this is that the leaching rate was higher than expected, the leaching fluid was saturated and the dissolved minerals precipitated. In principle, the minerals were dissolved and moved from one part of the fractures to precipitate at another part, causing clogging. The effect of the leaching field test has been simulated by means of a numerical model. The conclusion is that a leaching of rock as described in this paper should be combined with a deposition tank for the clogging material in order to avoid precipitation in the rock fractures. The results of this project have demonstrated a way of sealing rock fractures that has many more applications in engineering geology.
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