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  • 1
    Electronic Resource
    Electronic Resource
    Spheroidal dolomites in a Visean karst system – bacterial Induced origin? (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 44 (1997), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Spheroidal dolomite crystals occur in the karstified top of a Dinantian dolomite sequence in eastern Belgium. The spheroidal dolomite crystals are best developed at the base of the karst system. The dolomite crystals are characterized by a spherulitic or dumb-bell inclusion pattern, and are overgrown by dolomite cements with a rhombohedral outline. They are considered to be bacterially related precipitates based on, (1) textural similarities with documented bacteriogenic precipitates, (2) the presence of ‘bacterial’microspheres and framboidal pyrite embedded within the dolomite, and (3) their general geological setting. The geochemical characteristics of the dolomites and associated minerals support a bacterial origin. The ubiquity of framboidal pyrite, depleted in 34S (δ34S=— 22.4 to — 25.5%oCDT), testifies to a period of bacterial sulphate reduction. The isotopic composition of the spheroidal dolomites (δ13C=— 2.4 to - 3.2%oPDB and δ18O=— 3.8 to - 3.4%oPDB) suggest a contribution from oxidized organic carbon produced during bacterial sulphate reduction. Sulphate reduction may also result in a concomitant 18O depletion if the system is nearly closed. It is however, evident from the sulphur isotopic composition of associated framboidal pyrite that the system was fairly open. The 18O depletion of the spheroidal dolomite crystals (δ18O=— 3.8 to — 3.4%oPDB) and their occurrence adjacent to, and within karst cavities suggests a mixing zone origin, with a significant proportion of freshwater in it. The rhombohedral cement-overgrowths have calculated δ18O values in the range of 0 to +5.3%oPDB, which reflect precipitation from normal to slightly evaporated contemporaneous seawater.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1997.tb00431.x
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  • 2
    Electronic Resource
    Electronic Resource
    Origin of Dinantian zebra dolomites south of the Brabant-Wales Massif, Belgium (1998)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 45 (1998), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Zebra dolomites, characterized by a repetition of dark grey (a) and light (b) coloured dolomite sheets building up abbabba-sequences, occur in Dinantian strata from deep boreholes (〉 2000 m) south of the Brabant-Wales Massif in Belgium. These zebra dolomite sequences are several tens of metres thick. The dark grey dolomite sheets (a) consist of non-planar crystals, 80–150 μm in diameter. These crystals display a mottled red–orange luminescence and are interpreted to be replacive in origin. The white dolomite sheets (b) consist of coarse crystalline nonplanar b1 dolomite, which evolves outwards into transparent saddle shaped b2 dolomite. The b1 dolomites possess a mottled red–orange luminescence similar to the a dolomites, while the saddle shaped b2 rims display red to dark brown luminescent-zones. The b1 dolomites are possibly partly replacive and partly cavity filling. Their b2 rims display criteria typical for a cement origin. Locally, cavities exist between two succeeding white dolomite sheets. These cavities make up ≈5% of the zebra rocks and are locally filled by saddle shaped ankerite and/or xenomorphic ferroan calcite.Geochemical and fluid inclusion data (Th ≈ 120 °C) indicate a burial diagenetic origin for these zebra dolomites. The a and b1 dolomites are characterized by similar geochemical compositions and fluid inclusion data pointing toward a related origin. To explain the development of the zebra textures, suprahydrostatic pressures in conjunction with late Variscan tectonic compression are invoked. A model involving dolomitizing fluids expelled during the Variscan orogeny is proposed. An overpressured system is also invoked to explain the important porosity development, the creation of centimetre-scale subvertical displacements of the zebra pattern and the microfractures affecting the b1–b2 dolomite crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.1998.00171.x
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  • 3
    Electronic Resource
    Electronic Resource
    Multiple-step recrystallization within massive ancient dolomite units: an example from the Dinantian of Belgium (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 41 (1994), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: South of the Caledonian Brabant-Wales Massif a more than 200 m thick Tournaisian to Lower Visean replacive dolomite unit can be followed for several hundred kilometres from the Boulonnais (France) to Aachen (Germany). Field observations, of features such as karst cavities occurring at the top of the Lower Visean dolomite which are filled by Lower Visean crinoidal limestone, indicate that dolomitization and karstification took place during the Early Visean. This early development of the dolomite is in agreement with the presence of stylolites cutting the dolomite fabric. The minor element composition of the majority of the dolomites remains almost uniform throughout the entire studied area. Values for Fe, Mn, Na and Sr are normally in the range 700–4700 ppm, 15–400 ppm, 80–300 ppm and 50–200 ppm, respectively. The δ13C values (range-0.72 to +5.31%o) mainly reflect the carbon isotopic composition of the precursor limestones. The δ18O values, in contrast, are highly variable: ranging from-19.15 to +0.85%o. This rather large range of δ18O values is explained by multiple-step re-equilibration/recrystallization during progressive burial and subsequent uplift of the dolomites. These processes are also responsible for the high 87Sr/86Sr values of the dolomites which range from about 0.7088 to 0.7098. They are distinctly more radiogenic than Lower Visean marine carbonates (0.7076–0.7078). Correlation, however, of δ18O values or 87Sr/86Sr ratios with dolomite and/or cathodoluminescenec (CL) textures has not been very successful. This suggests that recrystallization may remain unrecognized if only petrographic techniques are used. Nevertheless, certain CL textures can be related to specific interactions with the ambient recrystallizing fluids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1994.tb02011.x
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  • 4
    Electronic Resource
    Electronic Resource
    Comment on the paper: ''A test of the reliability of the RbSr dates for selected glauconite morphologies of the upper cretaceous (Navesink formation) of New Jersey'', by R.L. Montag and D.E. Seidemann
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 58 (1982), S. 439-441 
    Details
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0012-821X(82)90092-9
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  • 5
    Electronic Resource
    Electronic Resource
    Evolution of palaeofluids at the Variscan thrust front in eastern Belgium (1998)
    Springer
    Geologische Rundschau 87 (1998), S. 373-380 
    Details
    ISSN: 0016-7835
    Keywords: Key words Fluid inclusions ; Palaeofluids ; Stable isotopes ; Variscan thrust front ; Vein cements
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The geochemical evolution of the fluids migra- ting at the Variscan thrust front in eastern Belgium has been investigated by a petrographic, mineralogical and geoche-mical study of ankerite, quartz and ferroan calcite veins hosted by lower Devonian rocks. Three vein generations have been recognized. The first generation consists of quartz, chlorite and ankerite filling pre- to early Variscan extensional fractures. The second generation is present as shear veins of Variscan age, and contains quartz, chlorite and ferroan calcite. The third generation consists of ankerite filling post-Variscan fractures. The oxygen and carbon isotopic composition of the two ankerite phases and of the ferroan calcites are respectively between –16.4 and –11.4‰ PDB between –17.8 and –1.7‰ PDB. This range is greater than that of calcite nodules in the lower Devonian siliciclastic sediments (δ18O= –15.6 to –11.1‰ PDB and δ13C= –13.4 to –10.2‰ PDB). This suggests precipitation of the carbonate veins from a fluid which was at most only partly isotopically buffered by the calcite nodules in the host rock. The calculated oxygen isotopic composition of the ambient fluid from which the calcite veins formed is between +7.8 and +10.0‰ SMOW. Two main fluid types have been recognized in fluid inclusions in the quartz and carbonates. The first fluid type is present as secondary fluid inclusions in the first and second vein generations. The fluid has a salinity of 0.5–7.2 eq. wt.% NaCl and a high, but variable, homogenization temperature (Th=124–188°C). Two origins can be proposed for this fluid. It could have been expelled from the lower Devonian or could have been derived from the metamorphic zone to the south of the area studied. Taking into account the microthermometric and stable-isotope data, and the regional geological setting, the fluid most likely originated from metamorphic rocks and interacted with the lower Devonian along its migration path. This is in agreement with numerical simulations of the palaeofluid and especially the palaeotempera-ture field, which is based on chlorite geothermometry and vitrinite reflectance data. The second fluid type occurs as secondary inclusions in the shear veins and as fluid inclusions of unknown origin in post-Variscan ankerite veins. Therefore, it has a post-Variscan age. The inclusions are characterized by a high salinity (18.6–22.9 eq. wt.% CaCl2). The composition of the fluid is similar to that which caused the development of Mississippi Valley-type Pb–Zn deposits in Belgium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310050216
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  • 6
    Electronic Resource
    Electronic Resource
    Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition (1999)
    Springer
    Biogeochemistry 47 (1999), S. 167-186 
    Details
    ISSN: 1573-515X
    Keywords: Zeeschelde ; stable carbon isotopes ; dissolved inorganic carbon ; particulate organic carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (δ13CPOC) and suspended matter (δ13CPOC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest δ13CDIC values are observed due to enhanced input of CO2 from decomposition of 13C-depleted terrestrial plant detritus (average δ13CDIC = −/14.3‰). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative δ13CDIC values (average δ13CDIC = −9.9‰). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a 〈 4.5 μgl−1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 μgl−1. Furthermore, in winter the very narrow range of δ13CPOC (from −26.5 to −27.6‰) is associated with relatively high C/N ratios (C/N 〉 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer δ13CPOC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N 〈 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in 13C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of 13C/12C fractionation by phytoplankton is attempted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006143827118
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  • 7
    Electronic Resource
    Electronic Resource
    Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition (1999)
    Springer
    Biogeochemistry 47 (1999), S. 167-186 
    Details
    ISSN: 1573-515X
    Keywords: Zeeschelde ; stable carbon isotopes ; dissolved inorganic carbon ; particulate organic carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (δ13 cdic) and suspended matter(δ 13 CPOC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest δ13 cdic values are observed due to enhanced input of CO2 from decomposition of13C-depleted terrestrial plant detritus (average δ13Cdic=-14.3‰). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative δ13Cdic values (average δ13Cdic =−9.9‰). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a 〈 4.5 μgl−1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 μgl−1. Furthermore, in winter the very narrow range of δ13 Cpoc (from -26.5 to -27.6‰) is associated with relatively high C/N ratios (C/N 〉 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer δ13 cpoc exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N〈 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in13C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of13C/12C fractionation by phytoplankton is attempted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00994921
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  • 8
    Electronic Resource
    Electronic Resource
    Origin and fate of dissolved inorganic carbon ininterstitial waters of two freshwater intertidalareas: A case study of the Scheldt Estuary, Belgium (2000)
    Springer
    Biogeochemistry 51 (2000), S. 141-160 
    Details
    ISSN: 1573-515X
    Keywords: Belgium ; DIC ; intertidal sediments ; methanogenesis ; Scheldt Estuary ; stable ; carbon isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Processes affecting the concentration and isotopiccomposition of dissolved inorganic carbon (DIC) wereinvestigated in pore waters of two freshwaterintertidal areas of the Scheldt Estuary, Belgium. Porewater δ13CDIC values from marshes andmudflats varied from −27 to +13.4‰, these very largevariations reflect the contribution of differentcarbon sources to the DIC pool. In pore waters of the upper mudflat, river water DICand dissolution of calcite contribute to a lesserextent (10% and 16% respectively) to the total DICpool. Results indicate that inorganic carbon added tothe pore water of the mudflats has a δ13Cvalue of +20.3‰ in May 1998. These strongly enrichedδ13CDIC values suggest that the majorcontribution (up to three-quarters) to total DIC isCO2 derived from methanogenesis. In pore waters of the marshes, CO2 derived fromorganic matter degradation (−27.5‰) and river DIC(−11.5 to −16.1‰) are the major sources of inorganiccarbon contribution to the total DIC pool. In porewaters from a marsh site colonised by willow trees,the contribution from CO2 derived from organicmatter degradation is larger than in pore waters froman area with only reed vegetation. In the latter caseriver water DIC is the major source of pore waterDIC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006472213070
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  • 9
    Electronic Resource
    Electronic Resource
    Petrography and geochemistry of septarian carbonate concretions from the Boom Clay Formation (Oligocene, Belgium) (1998)
    Springer
    Netherlands journal of geosciences 77 (1998), S. 63-76 
    Details
    ISSN: 1573-9708
    Keywords: bacterial sulphate reduction ; early diagenesis ; geochemistry ; stable isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The septarian carbonate concretions from the Boom Clay (Belgium) consist mainly of authigenic minerals such as micrite (≤ 70% bulk volume) and pyrite framboids (∼ 3%). These mineral phases occur between detrital grains and fossils. The septarian cracks are lined with calcite, which is sometimes covered with pyrite. The preservation of delicate sedimentological features in the concretion matrix (hardly compacted faecal pellets, burrows and uncrushed shells) points to an early origin of the concretions. Systematic geochemical variations from concretion centre to edge suggest that growth continued during shallow burial. Theδ13C values (−17.5 to −20.5‰) of the concretionary carbonate show that bacterial sulphate-reduction processes were dominant. Sulphate-reduction-derived HCO3- was diluted by marine-related HCO3-, derived from dissolved bioclasts. A slight enrichment in δ13C during growth is caused by the decreasing influence of sulphate reduction because of the progressive closure of the diagenetic system due to shallow-burial compaction. The δ18O values (−0.5 to +1.0‰) of the concretionary carbonate point to a marine origin. The slightly 18O-depleted signature with respect to time-equivalent marine-derived carbonate relates to the incorporation of an 18O-depleted component, originating from sulphate and organic matter. The slight decrease in δ18O during growth relates to an increasing influence of this component and to a decreasing influence of seawater-derived oxygen during early diagenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003468328212
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  • 10
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    Search for changes in groundwater flow as recorded by elemental changes in biogenic carbonates. (2016)
    Netherlands Institute of Ecology, Centre for Esturarine and Coastal Ecology | Yerseke, Netherlands
    Details
    Publication Date: 2021-05-19
    Description: Shells of gastropods and bivalves from different sites along the Kenyan coast were analysed for major, minor, trace element and isotopic composition. The aim was to assess the potential of shells to archive short term fluctuations of the physico-chemical characteristics of the environment in which they were thriving and to document differences between sites eventually related with differences in regime of groundwater and surface water flow. Focus was on the bivalve Isognomon sp. common to the area, but other species of bivalves and gastropods were analysed as well.
    Description: Published
    Keywords: Ground water ; Biogenic deposits ; Gastropod fisheries ; Shells ; Outflow waters
    Repository Name: AquaDocs
    Type: Report Section , Not Known
    Format: pp.115-131
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