RMZ - Materials and Geoenvironment, Vol. 52, No. I, 67-69, 2005
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Tracing the carbon cycle using stable isotopes of carbon in the Pliocene lignite Velenje basin, Slovenia
Tjaša Kanduč1, Jože Pezdič2, Marko Vrabec3, Simon Zavšek3, Marko Ranzinger3, Miloš Markič4, Jennifer McIntosh5, Lynn M. Walter6
'Jožef Stefan Institute, Jamova 39, SI - 1000 Ljubljana, Slovenia; tjasa.kanduc@ijs.si 2Department of Geology, University of Ljubljana, Aškerčeva 12, SI - 1000, Ljubljana, Slovenia Q Velenje Coal mine, Partizanska 78, SI - 3320 Velenje, Slovenia RGeological Survey of Slovenia, Dimičeva 14, SI 1000, Ljubljana, Slovenia 5Johns Hopkins University 3400 N. Charles St., Baltimore, MD 21218-2681 T University of Michigan, 1018 CC Little Building, Ann Arbor MI 48109
Abstract - Stable isotopes of carbon were used to trace processes during and after lignite formation in the Velenje basin. Geochemical studies revealed several genetic types of coalbed gases: microbial methane and COP, endogenic COP and COP originating from carbonates. It was found that 8I3C of different lignite lithotypes were mainly influenced by biogeochemical processes (gelification) at the early stage of biomass accumulation. Isotope composition of dissolved inorganic carbon (DIC) in Pliocene and Triassic aquifers indicates mixing of dissolution of carbonates and organic matter decomposition.
Key words: carbon isotopes, coalbed gases, lignite, aquifer, carbonate lens, Velenje basin
Measuring the 513C value of either carbonate or organic matter is related to the 513C value of its source, which is a function of the overall carbon cycle. The major reservoirs for carbon are organic carbon and carbonate carbon. Although the size of certain carbon reservoirs, such as the atmosphere, are relatively small, the fluxes in and out of these reservoirs can be quite high, so that their abundance can be important, as well as their carrying capacity between other reservoirs (Anderson and Arthur, 1983).
The aim of the study was to trace the carbon cycle in the Velenje basin in different phases by stable isotope techniques to help to determine processes of Pliocene lignite formation.
Sampling of coalbed water was performed in October 2003 at the mining areas of
Preloge and Skale from Pliocene and Triassic aquifers. Sampling of different lithotypes of lignite (Markic and Sachsenhofer, 1997) was performed in year 2002 at delivery and exit roadways in the Pesje, Preloge and Skale mining areas. Lenses of diagenetic carbonates were taken from fractured zones of the Sostanj fault system in the Preloge mining area. Sampling of coalbed gas was performed during the years 2000 - 2003 in the lignite seam in zones with no secondary effects from the coal mining area. "Free" gas (Kotarba, 1990) for geochemical analysis was collected from boreholes in evacuated ampoules using a metal capillary tube and plastic syringe.
The isotope composition of dissolved inorganic carbon (DIC) in water, diagenetic carbonates, methane as well as COp was determined using a Europa 20-20 continuous flow
Short scientific paper
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Kanduč, T. et al.
Atmosphere
Dissolu lion
Inorganic carbon cycle In the Velenje basin
DIC (dissolved inorganic carbon)
Carbonate lens
Figure I. Inorganic carbon cycle m the Velenje basin.
Figure 2. Organic carbon cycle in the Velenje basin.
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Tracing the carbon cycle using stable isotopes of carbon in the Pliocene lignite.
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isotope ratio mass spectrometer (CF - IRMS) with an ANCA - TG preparation module. Stable isotopes of carbon in different lithotypes of lignite were determined using a Europa 20-20 CF - IRMS with ANCA -SL module. The stable carbon isotopes are presented in the ô - notation relative to VPDB standards and expressed in %o. Analytical precision for carbon isotope composition is estimated to be ± 0.2 %.
Stable isotopic inorganic and organic cycles for the Velenje basin are shown on Figures I and 2. Stable isotope values of coalbed gases, carbonates and coal are due to isotopic frac-tionation and reflect all the processes occurring since lignite formation.
References
Anderson, T. F., Arthur, M. A. (1983): Stable isotopes of oxygen and carbon and their application to sedimentologic and paleoenvironmental problems, In: Arthur, M. A., Anderson, T. F., Kaplan, I. R., Veizer, J., and Land, L. S., eds., Stable isotopes in sedimentary geology, Volume 10: Columbia, SEPM Short Course, 1 - 1S1.
Kotarba, M.J. (1990): Isotopic geochemistry and habitat of the natural gases from the Upper Carboniferous Zacler coal - bearing formation in the Nowa Ruda coal district (Lower Silesia, Poland). Organic geochemistry, 16, S49 - S60.
Markic, M., Sachsenhofer, R.F. (1997): Petrographic composition and depositional environments of the Pliocene Velenje seam (Slovenia). International Journal of coal geology, 33, 229 -2S4.
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