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  • 1
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    Unravelling the shape and stratigraphy of a glacially-overdeepened valley with reflection seismic: the Lienz Basin (Austria) (2019)
    In:  Swiss Journal of Geosciences
    Details
    Publication Date: 2020-11-22
    Description: We reveal the subsurface bedrock topography and sedimentary succession of one of the deepest glacially-formed basins in the Eastern Alps: the Lienz Basin in the Upper Drau Valley (Tyrol), by means of seismic reflection. A dense source-receiver spacing, supplied by autonomous receivers, and a prestack depth-migration processing scheme were essential to distinguish the various deposits in fine detail, such as slumping, fan delta deposits, and a modified monocline on the basin flank. These details support our interpretation of the seismic stratigraphy that consists of, e.g., subglacial till of last glacial maximum (LGM) age and possibly older, laminated basin fines, and gravel/coarse sand. The maximum depth of the basin is 622 m, at the junction of two major basement faults that are not clearly visible in the seismic reflections. We regard the overdeepening in this longitudinal valley as the result of glacier confluence during the LGM. Subglacial meltwaters utilized the higher erodibility of faulted rocks, as indicated by channel structures. The adverse slope (2.6%) along the valley axis exceeds the gradient ice-surface slope (0.4–0.5%) during the LGM by more than fivefold. We thus suggest this feature is a product of a pre-LGM phase, since adverse slopes greater than ~ 1.2 times the ice surface slope promote the freezing of water in subglacial channels and prevent efficient water flushing of sediments. Integrating other studies allows us to estimate the local overdeepening of the Lienz Basin and that of the whole Upper Drau Valley to be 146 m and 530 m, respectively. At the beginning of lacustrine sedimentation, we estimate the paleo-water depth to be at least 216 m.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 2
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    Concretionary methane-seep carbonates and associated microbial communities in Black Sea sediments (2018)
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    Publication Date: 2021-04-25
    Description: Gas seeps in the euxinic northwestern Black Sea provide an excellent opportunity to study anaerobic, methane-based ecosystems with minimum interference from oxygen-dependent processes. An integrated approach using fluorescence- and electron microscopy, fluorescence in situ hybridization, lipid biomarkers, stable isotopes (δ13C), and petrography revealed insight into the anatomy of concretionary methane-derived carbonates currently forming within the sediment around seeps. Some of the carbonate concretions have been found to be surrounded by microbial mats. The mats harbour colonies of sulphate-reducing bacteria (DSS-group), and archaea (ANME-1), putative players in the anaerobic oxidation of methane. Isotopically-depleted lipid biomarkers indicate an uptake of methane carbon into the biomass of the mat biota. Microbial metabolism sustains the precipitation of concretionary carbonates, significantly depleted in 13C. The concretions consist of rectangularly orientated, rod- to dumbbell-shaped crystal aggregates made of fibrous high Mg-calcite. The sulphate-reducing bacteria exhibit intracellular storage inclusions, and magnetosomes with greigite (Fe3S4), indicating that iron cycling is involved in the metabolism of the microbial population. Transfer of Fe3+ into the cells is apparently mediated by abundant extracellular vesicles resembling known bacterial siderophore vesicles (marinobactine) in size (20 to 100 nm) and structure.
    Keywords: Seeps; Methane; Archaea; Magnetotactic bacteria; Carbonate concretions; Greigite; Black Sea ; 551
    Language: English
    Type: article , publishedVersion
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  • 3
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    Carbonate precipitation in the alkaline lake Specchio di Venere (Pantelleria Island, Italy) and the possible role of microbial mats (2016)
    Elsevier Science Limited
    Details
    Publication Date: 2017-04-04
    Description: Alkaline lakes like the hydrothermally affected lake Specchio di Venere (Pantelleria Island, Central Mediterranean) are typical geological settings harbouring calcified microbial mats. The present work is focused on the discrimination between biotic and abiotic processes driving carbonate precipitation in this lake, using hydrochemical, mineralogical and isotopic data. Hydrochemical analyses demonstrate that the lake is nearly 10 fold supersaturated with regard to aragonite and seasonally reaches hydromagnesite supersaturation. Microscopic observations depict organosedimentary laminated structures consisting of microbial communities and aragonitic precipitates, which are rather disseminated in pores than directly linked to microorganisms. Oxygen isotopic data indicate that authigenic carbonate crystallisation from evaporating water is the dominant precipitation process, further suggested by the absence of textural evidence of diagenetic processes. Conversely, the observed d13C values reflect an influence of extracellular polymeric substances (EPS) on carbon fractionation during the precipitation process, due to the selective sequestration of 12C in the biomass. The above considerations suggest that at lake Specchio di Venere the carbonate precipitation is mainly of inorganic nature, but a minor role played by biologically influenced processes in microbial mats is not excluded.
    Description: Published
    Description: 168-176
    Description: 4V. Vulcani e ambiente
    Description: JCR Journal
    Description: restricted
    Keywords: alkaline lake ; carbonate precipitation ; hydrochemistry ; Pantelleria ; 03. Hydrosphere::03.01. General::03.01.07. Physical and biogeochemical interactions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Miniaturized biosignature analysis reveals implications for the formation of cold seep carbonates at Hydrate Ridge (off Oregon, USA) (2018)
    Details
    Publication Date: 2021-03-29
    Description: Methane-related carbonates from Hydrate Ridge typically show several macroscopically distinguishable mineral phases, namely whitish aragonite, lucent aragonite, and gray micrite. The relationship of these phases to particular microorganisms or biogeochemical processes is as yet unclear. We used a miniaturized biomarker technique on mg samples, combined with factor analysis and subsequent electron microprobe analysis, to study lipid biomarkers and chemical compositions of the individual phases. This allows us to identify particular mechanisms involved in the formation of the different carbonate precipitates. Our combined analysis of biomarkers and petrographic traits shows that most of the lipids related to the anaerobic oxidation of methane (〉90% by weight) are concentrated within only a minor compartment ( 20% by volume) of the Hydrate Ridge carbonates, the whitish aragonite. The patterns indicate that the whitish aragonite represents fossilized biofilms of methanotrophic consortia containing mainly archaea of the ANME-2 group and sulfate reducing bacteria, whereas the precipitation of the lucent aragonite may have lacked the immediate proximity of microorganisms during formation. By contrast, the gray micrite formed by incorporation of allochthonous organic and inorganic matter during carbonate precipitation induced by the anaerobic oxidation of methane involving ANME-1 archaea.
    Keywords: mineral phases; ANME-1 archaea ; 551
    Language: English
    Type: article , publishedVersion
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