Three different lithotypes (xylitic, gelified and matrix) of Pliocene lignite from the Velenje Basin, Slovenia, were investigated to establish the variations of biomarker compositions in solvent ...extracts and the stable isotope (carbon and nitrogen) compositions of bulk material. From the biomarker results, the xylitic lithotype almost exclusively originates from gymnosperms (conifers such as Taxodiaceae), as indicated by the very high contents of sesquiterpenoids and diterpenoids but very low abundances of n-alkanes and non-hopanoid triterpenoids. The relative proportion of gymnosperms to angiosperms in the paleomire is reflected by the ratio of diterpenoids to the sum of diterpenoids and non-hopanoid triterpenoids (Di-/(Di-+Tri-terpenoids)), which is close to 1 (av. 0.99) in the xylitic lithotype. The predominance of diterpenoids from conifers in the xylitic lithotype is associated with high C/N ratios and intermediate total sulfur (TS). The very low abundance of hop-17(21)-ene and the absence of further hopanoids in the xylitic lithotype indicate a restricted influence of bacterial degradation under relatively dry conditions in the paleomire. The matrix lithotype also originated preferentially from gymnosperms under dry depositional conditions, as indicated by the high Di-/(Di-+Tri-terpenoids) ratio (0.95), low amounts of hopanoids and low TS content. The gelified lithotype is characterized by a high content of n-alkanes and wide variation of the Di-/(Di-+Tri-terpenoids) ratio (0.13–0.88), indicating a fluctuating contribution of angiosperms to the plant community in the paleomire during formation of this lithotype. In addition, the high abundance of hop-17(21)-ene and TS in the gelified lithotype compared with the other two lithotypes suggests the effect of bacterial activity under relatively wet/humid conditions during formation of the gelified lithotype, which is also supported by the considerable content of mid-chain n-alkanes.
The high correlation between the δ13C and δ15N values (R2 = 0.68) indicates that the stable carbon and nitrogen isotope composition in the Velenje lignites were probably influenced by the same factors (e.g. precursor plants and/or microbial activity). The stable carbon isotopic values (av. −25.44‰) and nitrogen isotopic values (av. 2.15‰) of the xylitic lithotype are higher than those of the gelified lithotype (av. δ13C = −27.48‰, δ15N = 1.37‰) and the matrix lithotype (av. δ13C = −27.09‰, δ15N = 1.10‰). The relatively high correlation between the diterpenoid content and both δ13C and δ15N values suggests that the stable carbon and nitrogen isotopic composition of the three lithotypes might reflect the composition of the original plant material in the paleomire. The dominance of conifers as precursor plants in the xylitic lithotype might be the main reason for the higher δ13C values and probably also the higher δ15N values. The relatively higher δ15N values in the xylitic lithotype than in the other types could be explained by the high amount of decay-resistant xylem and low mineral (e.g. clay) content in the xylitic lithotype. The slightly lower δ13C but higher δ15N values in the gelified lithotype than in the matrix lithotype can be explained by variation of parent plant materials and the influence of bacterial activity.
•Different lithotypes (xylitic, gelified and matrix) of Pliocene lignite from the Velenje Basin, Slovenia, were analyzed for biomarkers and stable isotope (C and N) compositions.•The ratio of diterpenoids/(diterpenoids + triterpenoids) reflects the relative proportions of gymnosperms and angiosperms.•Xylitic and matrix lithotypes originate from gymnosperms, while gelified lithotypes are characterized by a fluctuating contribution of angiosperms.•The highest δ13C and δ15N values were measured in xylitic lithotype samples.•The δ13C and δ15N composition is preferentially influenced by the composition of the precursor plants community.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
High contents of arsenic (As) in coal samples from four localities within Neogene deposits of the Pannonian Basin in Slovenia are presented and discussed in this paper. Data from three localities ...represent interval samples of coal cuttings from wells TER-1 (Terbegovci), Sob-3g (Murska Sobota), and MD-1 (Mislinjska Dobrava). The fourth locality is Globoko, where the main lignite seam was analysed already in 1989. The oldest are coal samples from the MD-1 well which are supposed to be of the Lower Miocene age (except for the shallowest one, which is of the Plio-Quaternary age). Coal samples from the TER-1 and Sob-3g wells are of the Upper Miocene age (Mura Formation). The lignite sample from Globoko is of the Upper Miocene age too (Pontian; Globoko Formation). Most samples were prepared for the ICP-MS method analysis as “whole coal”, dry, pulverized lab-samples, weighting ca. 10 g. The results show for all “whole coals” samples considerably increased contents of As: 22.7, 111.4, 222.1, and 131.4 µg/g for the Lower Miocene (?), and 84.5 µg/g for the Plio-Quaternary coals from MD-1 well, 392 µg/g for coals from the Sob-3g well, and 116 µg/g for a coal from the TER-1 well (both Upper Miocene – Mura Formation). In the case of Globoko, not “whole coal” but its high temperature ash was analysed and showed As content as high as 170 µg/g applying AAS method of analysis, and even 260 µg/g applying the ICP-MS. Origin of As could be pre-Neogene rocks of the hinterland and/or Neogene calc-alkaline volcanites. Mineral-gas exhalations from the under-continental upper mantle, containing As, could also be a source of this highly volatile element.
Upper Triassic (Carnian - Julian) bedded dark limestone in the Lesno Brdo area, more precisely in the Drenov Grič quarry (Central Slovenia), was investigated in this study to describe its carbonate ...facies, its geochemical characteristics of the inorganic and organic matter, and to estimate its hydrocarbons generative potential. The site was chosen as a well referenced location of previous lithological and paleontological studies with the aim to fill a gap in the up-to-date knowledge on organic petrology of the investigated rocks termed as the Julian “Carbonate Member” within the Lesno Brdo stratigraphic sequence. The study represents the first multi-analytical organic petrological investigation of Mesozoic carbonate rocks in Slovenia. In the Drenov Grič (DRG) section, 7 microfacies were defined. A total of 38 DRG samples of micritic limestones, marlstones, and a coaly sample were collected from the section. The average total organic carbon (TOC) content of the samples is 0.70 wt% with one outstanding sample DRG-28 with a TOC content of 15.56 wt.%. According to the TOC content, DRG samples are considered as a fair to good source rock for hydrocarbons generation. In addition, the samples with TOC >0.5 wt.% were characterised by the Rock-Eval S1, S2 and S3 peaks, hydrogen and oxygen indices (HI, OI), Tmax and production index (PI) values. According to these data, typical “black” Julian carbonate beds from the Drenov Grič locality are poor source rocks. Based on pyrolysis data (HI versus OI), the type of the organic matter could not be determined, so a micropetrographic examination was performed. . The predominant and the only clearly visible maceral in the DRG samples is vitrinite within the amorphous organic matter. Given the low S2 peaks, thermal maturity was determined by vitrinite reflectance. Vitrinite reflectance results (between 2.71 ± 0.19 %Ro and 3.89 ± 0.17 %Ro) indicate that the organic matter in the DRG samples is in a thermally mature to overmature stage, which is also consistent with the Thermal Alteration Index (TAI) (4- - 4). All 38 samples were also analysed on main and trace elements, focusing on the redox sensitive trace elements (Ni, Mo, Th, U, V and Zn) to supplementary interpret depositional conditions. Overall, the “black” carbonate rocks of the Drenov Grič section show a negligible potential for the generation of hydrocarbons. Their original dispersed organic matter was thermally strongly transformed. Therefore, the investigated carbonate rocks almost completely exhausted their ability to generate a considerable quantity of hydrocarbons. They can therefore be classified as “spent source rocks”, which could conditionally generate some dry gas.
•Terrigenous organic matter dominates in Carnian black limestone in Lesno Brdo area (Slovenia).•Organic matter is (paleothermally) overmature.•Black limestone shows negligible hydrocarbons generative potential.•Only dry gas could be generated from these carbonate rocks.•Redox conditions during deposition of black limestones were in general to suboxic.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The carbon isotopic composition of methane (δ13CCH4) in natural gas from the Petišovci-Dolina oil and gas field (NE Slovenia) was measured for the first time in August and September 2021. The gas ...samples from different depths were taken from three wells: Dolina-deep (Pg-6) from the depth interval 3102–3104 m, Petišovci-deep (Pg-5) from the depth interval 2772–2795 m, and Petišovci-shallow (D-5) from the depth interval 1212–1250 m. According to the available composition dataset of gas, available from the Petrol Geo d.o.o. documentation, the “deep” gases sampled from the Pg-6 and Pg-5 wells consist of 85 % methane (C1), 11 % hydrocarbons heavier than methane (C2–C6) and 4 % CO2. The “shallow” gas from well D-5 contains more than 89 % methane, up to 11 % C2–C6 gases, while the CO2 content is negligible. The “deep« gas from the Pg-6 and Pg-5 wells has δ13CCH4 -36.7 ‰ and -36.6 ‰, respectively, while the “shallow” gas from the D-5 well has the δ13CCH4 of -38.6 ‰. The methane from the “shallow” gas is slightly enriched in the lighter 12C isotope. δ13CCH4 in the range from -38.6 to -36.6 ‰ clearly indicates the thermogenic origin of methane formed during the catagenesis phase of gas formation.
This study investigates the carbon (δ13Corg) and nitrogen (δ15N) isotopic composition of tertiary lignites and coals from six sedimentary basins: Velenje, Mura-Zala, and Zasavje in Slovenia; Sokolov ...in Czech Republic, Barito in Indonesia; and Istria in Croatia. The aim is to investigate the correlation between the fine detrital (fD) component and δ13C and δ15N in Velenje lignite samples. Additionally, we aim to evaluate the biogeochemical processes of organic substances during their deposition in all analyzed samples, calculate their δ13CCO2 values and compare the analyzed values of δ13C and δ15N to those reported in the literature. Thirty-two samples were analyzed, predominantly from the Velenje ortho-lignite (Pliocene), with additional lignites and coals from the Pannonian to Paleocene epochs for comparison. Carbon isotopic composition (δ13Corg) ranged from -27.9 to -23.6 ‰, and nitrogen isotopic composition (δ15N) ranged from 1.8 to 7.4 ‰. The fine-detrital lithotypes of the Velenje ortho-lignite exhibited the most negative δ13Corg values due to anaerobic bacterial activity in an intramontane alkaline lake environment influenced by the carbonate hinterland. Moreover, gelification processes affected fine-detrital organic matter more than larger wooden pieces. Terbegovci, Hrastnik meta-lignites, and Barito sub-bituminous coal also displayed low δ13Corg values, indicating limited gelification, while variations in the δ15N values suggested differences in mineralization. The Velenje xylitic lithotypes have higher δ15N values, indicating a more intense mineralization under aerobic conditions. Raša ortho-bituminous coal, deposited in a brackish environment, displayed the highest δ13Corg values and a wide range of δ15N values due to fluctuating water tables in a paralic carbonate platform environment. The lowest δ15N value was observed in the Sokolov Basin lignite coal, indicating minimal mineralization and low bacterial activity. The isotopic composition of CO2 in air (δ13Cair), which was calculated using the δ13C values in lignites and coal, ranged from -8.4 to -3.4 ‰, with Velenje lignite displaying the minimum value and Raša coal showing the maximum value. The determined δ13C and δ15N values of the coal and lignite samples in this research fall within the typical range of world coals.
A composite sample of coal cuttings (depth: 141.0–155.5 m) from the TER-1/03 water supply well in northeastern (NE) Slovenia (Slovenske gorice; locality Terbegovci – Sveti Jurij ob Š~avnici) was ...analysed for its coal quality (proximate analysis – percent moisture, volatile matter, fixed carbon, ash), calorific value, and major (C, H, O, N, S)-, minor (Si, Al, Fe, Mg, Ca, Na, K, Ti, P, Mn – as oxides)- and trace-elemental (43 elements) chemical composition. The coal was classified as a “normal” humic, high-grade metalignite, similar to coals in the Mura Formation of the Mura-Zala Basin. Unusually high arsenic (As) content of more than 100 µg/g was determined in the investigated coal matter, whereas the Clarke value for the world coals is between 5 and 10 µ g/g, as cited by different authors. Besides As, also Sb, V, Mo, U, and W have been found to be enriched in the studied coal.
The paper presents the results of granulometrical, geochemical and mineralogical characterisation of sediments underlying the Velenje lignite seam as drilled through the P-9k/92 borehole in the ...central part of the Pliocene intermontane Velenje Basin. This study of differently lithified sediments/sedimentary rocks is based on analyses of 32 samples from 21 core intervals at the depth of 562.6–580.0 m (end of the borehole). Grain size was analysed on 12 samples, 24 samples were investigated geochemically, while mineral composition was obtained with X-ray diffraction (XRD) on 23 samples, and optical microscopy was performed on 7 samples. Granulometry of very low lithified samples revealed that they are mostly clayey silts (>85 % of the silt fraction), only two are silty sands and one is pebbly/rubbly sandstone. Well-lithified clastics are all sandstones cemented by calcite, siderite and/or marcasite. Geochemical analysis indicated that most samples are SiO2 + Al2O3 rich (>60–80 %). Some sediments, mostly at the base of the profile, are enriched in Fe2O3 and inorganic C both indicating the presence of siderite. At the top of the profile, thin limestone and gravelly sandstone beds contain a high CaO content and have high loss on ignition (LOI). Qualitative XRD analysis and microscopy showed that all clastic sediments consist of quartz, kaolinite and muscovite/illite. Feldspars occur sporadically, mainly in sands and sandstones. Gypsum was found in some samples of siltstones. Pyrite occurs only in a sample of limestone at the top of the profile. Also marcasite was found only in one sample.
Stable isotopes of carbon were used to trace organic and inorganic carbon cycles and biogeochemical processes, especially methanogenesis within different geologic substrates of the Pliocene ...lignite-bearing Velenje Basin in northern Slovenia. Lithotypes of lignite, coalbed gases, calcified woods (xylites), carbonate-rich sediments, and groundwaters were investigated. Carbon isotope (δ13C) values of the different lignite lithotypes ranged from −28.1 to −23.0‰, with the variability likely a function of the original isotopic heterogeneity of the source plant materials and subsequent biogeochemical processes (i.e. gelification, fusinitization, mineralization of organic matter) during the early stage of biomass accumulation and diagenesis. In the lignite seam, CO2 and CH4 were the major gas components with small amounts of N2. The carbon isotope values of CO2 (δ13CCO2) and CH4 (δ13CCH4) were highly variable, ranging from −9.7 to 0.6‰ and −70.5 to −34.2‰, respectively. Carbon dioxide is likely sourced from a mixture of in situ microbial activity and external CO2, while CH4 is dominantly sourced from microbial methanogenesis, with possible addition of thermogenic gas from deeper formations, and the influence of microbial oxidation of methane. Calcified xylites enriched with 13C (δ13C values up to 16.7‰) indicate that microbial methanogenesis was active during formation of the basin. The δ13CDIC values (from −17.4 to −3.2‰) of groundwaters recharging the basin from the Triassic aquifer are consistent with degradation of organic matter and dissolution of dolomite. Groundwaters from the Pliocene sandy and Lithotamnium carbonate aquifers have δ13CDIC values (from −9.1 to 0.2‰) suggestive of degradation of organic matter and enrichment via microbial reduction of CO2.
► In this study we examine carbon cycling in Coal Basin. ► We study stable carbon isotopes in different geological media. ► Majority of methane was generated via microbial methanogenesis. ► Calcite precipitation was driven by microbial methanogenesis via CO2 reduction. ► Highly alkaline waters in the basin provide further evidence of microbial methane.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The study is based on 30 lignite, 6 footwall and 3 hanging-wall interval samples. Lignite seam of the Pliocene age is 101 m thick in the treated profile.Minorelementgeochemistryis evaluated by the ...contents of 11 standard oxides, among which SiO2, Al2O3, Fe2O3 and CaO form the bulk composition. Trace-element characterization is based on contents of 46 elements. Stot., Ctot., Corg. and loss on ignition (LOI) at 1000 ˚C were analysed in addition. All analyses (by ICP-AES, ICP-MS, Leco) were carried out on the “whole lignite”/“whole rock” samples in the Acme Analytical Laboratories (Canada). Recalculation to the “pure inorganic matter” basis was carried out in order to obtain realistic relations between contentsof minor element oxides. Contents of the minor element oxides in the inorganic matter are dependant on the ash content, and, an ash content of 20-25 % was found out as an important “geochemical threshold”. SiO2 + Al2O3, together with positively corelated K2O and TiO2, increase with increasing ash content. On the contrary, CaO, MgO and Fe2O3, they increase with decreasing ash content. Affinity of organic binding of Ca,Mg,and(probably)of Fe is ascertained by negligible contents of Cinorg. Abundances of the great majority of trace elements are mostly lower and/or normal in comparison to the world coals. However, As, U, and Mo are typomorphic for the treated lignite. In spite of that, they are not critical. Widespread areas of different lithologies with higher contents of these elements are known throughout the world as well as in Slovenia.
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