Reinhard Gratzer

Paleoenvironmental implications from biomarker and stable isotope investigations on the Pliocene Velenje lignite seam (Slovenia)

A Pliocene lignite seam up to 160 m thick occurs in the Velenje basin (Slovenia). The seam originated in a topogenous mire and evolved within a non-marine, transgressive setting. Differences in soluble organic matter yield and hydrocarbon content of borehole samples from the lignite are related to differences in the composition of free lipids of microbial origin and/or hydrocarbons derived from the biogeochemical degradation of plant tissue. Variations of the redox conditions within the mire are reflected by pristane/phytane ratios. The abundance of terpenoid biomarkers indicates the predominance of gymnosperms over angiosperms, which is consistent with palynomorphic spectra dominated by pollen of the Sequoia-Taxodium-Metasequoia plant community rather than by angiosperms. Evidence is also provided that the content of land plant derived biomarkers and the preservation of plant tissue is controlled by the input of resin-rich, decay-resistant conifers. Sections of the seam characterized by a high degree of gelification of humotelinite (gelification index) show high contents of hop-17(21)-ene but low hopane concentrations. The results suggest that the gelification of plant tissue may be governed by the activity of anaerobic rather than aerobic bacteria. Despite the minor variation in the proportions of gymnosperms versus angiosperms in the peat-forming vegetation, a general influence of the floral assemblage on carbon isotopic composition of the coals (δ13C=−25.3 to −27.0‰) is proposed. Carbon cycling during biogeochemical decomposition of plant tissue by bacteria is assumed to affect the δ13C value of the lignite. Petrographic and geochemical data of gelified and ungelified fossil wood provide evidence that gelification may be governed by microorganisms (e.g. anaerobic bacteria) different from those responsible for decreasing cellulose contents during early diagenetic, aerobic degradation of wood. Based on the molecular composition of terpenoid biomarkers, the wood fragments are identified as derived from gymnosperms. The relative proportions of saturated versus aromatic hydrocarbon fractions of fossil gymnosperms display a general tendency towards lower values in gelified wood remains. This indicates that bacteria involved in gelification of plant tissue may also be involved in aromatisation of diterpenoid hydrocarbons. The chemotaxonomical classification of the macrofossils as gymnosperms is corroborated by the mean carbon isotopic compositions of the macrofossils (δ13C=−24.5‰) and the extracted cellulose (δ13C=−22.0‰). The higher isotopic difference of about 2.5‰ between cellulose and fossil wood, compared to that found in modern trees, can most probably be explained by the smaller effect of 13C discrimination for cellulose when compared with wood during decomposition [Chem. Geol. 158 (1999) 121]. Compared with the coals, the δ13C values of wood and extracted cellulose are affected to a minor extent by microbial activity.

Depositional environment of the Late Miocene Hausruck lignite (Alpine Foreland Basin): Insights from petrography, organic geochemistry, and stable carbon isotopes

Abstract Lignites and fossil wood from two boreholes in the late Miocene Hausruck district (Alpine Foreland Basin, Austria) were investigated with respect to organic carbon and total sulfur contents, ash yields, maceral composition, organic geochemistry, and stable carbon isotope ratios. The lignites from the two sampled profiles differ in sulfur contents and petrography-based facies indicators (gelification index [GI], tissue preservation index [TPI]). The results point to drier and more acidic conditions in the part of the mire sampled at drill site Lukasberg, whereas the lignites from Kalletsberg formed under near neutral conditions due to a raised (ground) water table. The different depositional environments are supported by the paleogeographic positions of the boreholes: borehole Lukasberg is located within a paleo-valley, whereas borehole Kalletsberg is located at the deeper part of a basin situated south and southwest of the Hausruck area. Environmental changes with time within the mire are confirmed by the molecular composition of the soluble organic matter (SOM). Differences in pristane/phytane ratio, isomerisation of hopanes at position 17, concentrations of hopanes, and in the ratio of hopanes to hop-17(21)-enes are related to the extent of gelification of plant tissue, sulfur content and pH values, caused by differences in (ground) water table. The variable contents of individual terpenoid hydrocarbons derived from land plants indicate that angiosperms and conifers contribute to peat formation in the Hausruck district in variable proportions. Overall, angiosperm biomarkers slightly predominate. The tissue preservation index (TPI) within the Kalletsberg profile is probably governed by the proportion of decay-resistant conifers, as indicated by the correlation between TPI and biomarker composition of the coals. Correlations between δ 13 C values of the lignites (between −24.9‰ and −27.4‰) and their non-hopanoid terpenoid composition indicate the major influence of changes in peat-forming vegetation on the carbon isotopic composition of the coals in the Hausruck district. Carbon isotope data of macrofossils are consistent with their taxonomical classification as conifers ( δ 13 C between −22.7‰ and −25.1‰) and angiosperms ( δ 13 C between −25.5‰ and −26.6‰), respectively. The δ 13 C data of the extracted cellulose reveal clear differences between fossil wood from gymnosperms (average δ 13 C=−21.0‰) and angiosperms (mean δ 13 C=−23.4‰).

Organic geochemistry of the Lower Miocene Oberdorf lignite (Styrian Basin, Austria): its relation to petrography, palynology and the palaeoenvironment

Abstract In the Oberdorf trough at the northwestern margin of the Styrian Basin (Austria), an up to 36-m thick Lower Miocene (Ottnangian) lignite seam occurs within the fluvial Koflach–Voitsberg Formation. Previous results indicate that the lignite originated in a topogenous mire within a wet-forest swamp palaeoenvironment. Differences in soluble organic matter (SOM) yield of borehole samples from the lignite seam are related to free lipids present in plant waxes or resins and the presence of thermally labile polymers indicated by the contents of liptinite macerals (i.e., resinite, suberinite, and liptodetrinite). The n -alkane distribution patterns are dominated by high-molecular weight lipids with marked odd over even predominance, originating from plant waxes. A contribution of algae to the even numbered short-chain lipids, observed in considerable amounts in the footwall sediments is proposed. Terpenoid biomarkers characteristic for conifers and angiosperms were detected, consistent with palynomorphic spectra which are dominated by forest swamp pollen (Taxodiaceae–Cupressaceae) and pollen from plants living in a mixed mesophytic forest. Excellent relationships between higher plant biomarker composition and palynologic data indicate that the organic geochemical results reflect the varying inputs of coniferales vs. angiosperms. The data further imply that cuparene may be used for taxonomical differentiation of coniferales families. Organic geochemical data provide evidence that the content of land plant-derived biomarkers is controlled by the input of resin-rich conifers. Concentrations of hopanoids, dominated by hop-17(21)-ene, generally increase towards the top of the lignite, a section characterised by high extents of aromatisation of triterpenoid biomarkers. The results suggest that the aromatisation of angiosperm-derived biomarkers may be governed by the activity of anaerobic rather than by aerobic bacteria. However, changes in the depositional environment and palynologic facies during peat formation probably influenced the origin and fate of angiosperm-derived triterpenoids. The results indicate how biomarker composition may contribute to the evaluation of environmental changes. Cross-correlations of organic geochemical parameters with palynological data and petrography-based facies indicators will provide further insights in the peat-forming vegetation and biogeochemical activities in the mire.

Parameters determining the carbon isotopic composition of coal and fossil wood in the Early Miocene Oberdorf lignite seam (Styrian Basin, Austria)

Abstract Petrographical and geochemical data of gelified and ungelified fossil wood from the Early Miocene Oberdorf lignite seam (Styrian Basin, Austria) provide evidence that the early diagenetic, aerobic degradation of wood by fungi may be followed by further decomposition under reducing conditions by the activity of anaerobic bacteria. Based on the molecular compositions of terpenoid hydrocarbons, the wood fragments in the lignite are identified as gymnosperms. This result is corroborated by the mean isotopic composition (δ13C=-24.2‰) of the macrofossils. The isotopic difference between fossil wood and extracted cellulose of most samples (3.9–2.5‰) is higher than in modern trees, which can be explained by the smaller effect of 13C discrimination during decomposition of cellulose when compared with wood. The mean carbon isotope values found for gymnosperms and coals (−24.2‰ and –24.7‰, respectively) confirm the results from biomarker analyses indicating that the peat-forming vegetation of the Oberdorf seam was dominated by gymnosperm taxa. Minor variation in the relative contributions of gymnosperms and angiosperms to coal deposition is of negligible influence on the isotopic composition of the coals. Cross-correlations between δ13C of the coals, soluble organic matter yield, and the proportions of liptinite macerals of higher-plant origin imply that the carbon isotopic composition may be affected by the contents of plant lipids because of their δ13C values ranging from 5 to 10‰ less than whole-plant tissue values. An isotopic shift of the coals towards more negative values due to the activity of prokaryotes (i.e. anaerobic bacteria) in organic matter degradation is proposed. The results obtained from the Early Miocene Oberdorf lignite indicate that the carbon isotope ratios of the coals are primarily affected by varying contributions of different parts of whole-plant tissue, due to their different isotopic and molecular compositions (e.g. epicuticular leaf waxes, resins, wood) and their different decay-resistance against the early diagenetic changes involved in organic matter decomposition. Carbon cycling during anoxic decomposition of plant-derived organic matter is assumed to affect the δ13C values of coal. δ13C values of wood and extracted cellulose are affected only to a minor extent.

Organic geochemical and stable carbon isotopic investigation of coals formed in low-lying and raised mires within the Eastern Alps (Austria)

Abstract Up to 16 m thick coal seams formed in Miocene pull-apart basins within the Eastern Alps in low-lying and raised mires. Despite similar rank (sub-bituminous stage), coal quality differs significantly. Coals from low-lying mires (e.g. Fohnsdorf) are characterized by significantly higher ash yields and sulfur contents than coals from raised mires (e.g. Leoben). Organic geochemical and carbon isotope investigations were performed to assess the differences in facies. The Fohnsdorf coals are characterized by higher yields of soluble organic matter (SOM), slightly higher proportions of hydrocarbons in the SOM, generally lower pristane / phytane ratios, and the occurrence of high Corg-normalized n-alkane concentrations. Only n-alkane patterns in the Leoben samples show a marked odd over even predominance. These differences are indicative of a more intensive, dys- to anaerobic biochemical degradation of plant material within the Fohnsdorf mire. Terpenoid biomarkers characteristic of conifers and angiosperms were detected in the Leoben coals, whereas the latter are missing in the Fohnsdorf samples. In the Leoben coals higher saturated to aromatic diterpenoid ratios were detected than in the Fohnsdorf coals. Because of similar rank, enhanced aromatisation in the Fohnsdorf basin is probably related to microbial activity. Despite this, the Fohnsdorf coals are characterized by lower hopane concentrations. The results imply that the aromatisation of terpenoid biomarkers is governed by the activity of anaerobic rather than aerobic bacteria. An overall negative correlation between δ13C of organic matter and the degree of aromatisation of diterpenoid biomarkers is observed. It is suggested that the carbon isotopic composition results from different extents of microbial degradation of the biomass. The Fohnsdorf coals are rich in sulfur. High contents of coalbed methane were encountered during mining, suggesting high activities of anaerobic bacteria in a nearly neutral, sulfate-bearing (brackish) environment of the low-lying mire and methanogenesis during or after coalification. Sulfate-reduction and methanogenesis are known to increase δ13C values of residual organic matter.

Variable alteration of organic matter in relation to metal zoning at the Rote Fäule front (Lubin-Sieroszowice mining district, SW Poland)

Abstract Drill core samples of the Lower Zechstein strata in the Lubin-Sieroszowice Cu-mining district (SW Poland) were collected at different distances to the oxidized zone (Rote Faule), developed around the Zary Pericline. The sampled intervals include Kupferschiefer, underlying Weissliegendes sandstone and overlying Zechstein Limestone from Rote Faule zones, adjacent Cu-mineralized strata, and drill cores from the Pb/Zn-mineralized zone more distant to the Rote Faule front. The Kupferschiefer samples show differences in base metal and noble metal contents, accompanied by variations in the molecular composition of hydrocarbons. Organic matter is characterized by the soluble organic matter (SOM) yields, and relative proportions of saturated and aromatic hydrocarbons of the SOM. Our results provide evidence for an oxidative alteration of organic matter in Kupferschiefer samples within and adjacent to the Rote Faule zones. The extent of this alteration is reflected by differences in the composition of the saturated and aromatic hydrocarbon fractions of the soluble organic matter. In contrast to Kupferschiefer from Pb/Zn-mineralized areas, short-chain n-alkanes dominate the saturated hydrocarbons of oxidized samples. With decreasing distance to the Rote Faule zone, compositional changes of the aromatic hydrocarbon fractions are characterized by the increase in concentration of polycyclic aromatic hydrocarbons and elevated ratios of phenanthrene to methylphenanthrenes, resulting in a decrease of the methylphenanthrene index (MPI 1). In highly oxidized samples, the increase in the ratio of phenanthrene to methylphenanthrenes concentrations due to demethylation reactions appears to be reversed, probably caused by degradation of phenanthrene as well as the methylphenanthrenes. Organic matter of noble metal-bearing Kupferschiefer from the Rote Faule front is characterized by high abundances of polycyclic aromatic hydrocarbons (PAHs) and sulfur- and oxygen-bearing PAHs. This result might argue for a concomitant transport of the PAHs and the noble metals in ascending oxidizing solutions, and a contribution of metal-organic complexes in mobilisation and transport of gold. The regional base metal zonation in the Kupferschiefer inside the mines, is explained by redox controlled metal precipitation from oxidizing brines through decreasing Eh-conditions during its infiltration into the reduced Kupferschiefer. Short-scale zonation in Au and Pt/Pd-contents at the oxidized-reduced interface is consistent with that model of ore formation. Organic geochemical maturation parameters argue for maximum temperatures during Kupferschiefer diagenesis between 100 and 120°C. Comparable temperatures are assumed for the ore fluids responsible for Cu mineralization near Rote Faule.

Chemical characteristics of Upper Cretaceous (Turonian) jet of the Gosau Group of Gams/Hieflau (Styria, Austria)

Abstract Jet and coaly sediments within the Upper Cretaceous (Gosau) Schoenleiten Formation were collected from two outcrops near Gams/Hieflau (Styria, Austria). For comparison, additional jet and coal samples from different Gosau localities were included in the study. The identification of jet as bituminous driftwood (collotelinite) has been provided by microscopical examination of organic matter [Kollmann, H.A. and Sachsenhofer, R.F., Mitt. Ref. Geol. und Palaont. Landesmuseum Joanneum SH 2 (1998) 223]. Rock–Eval analyses revealed enhanced HI and lower T max values of jet compared with the coals and coaly shales. The results reflect the higher contents of bituminous organic matter compared to vitrain-rich coals of similar maturity. In comparison with the coals and coaly shales, high amounts of liberated hydrocarbons (mg HC/g C org ) are in contrast to generally lower yields of soluble organic matter during extraction with dichloromethane, indicating that portions of the hydrocarbons are liberated from lipids loosely bound to kerogen during pyrolysis. Further differences in n -alkane distribution patterns, odd over even predominance, pristane/phytane, and pristane/ n -C 17 ratios exist between jet, coals and coaly shales. The microbial origin of short-chain n -alkanes presumably resulted from the degradation of the predominant odd-numbered long-chain n -alkanes within the jet. The occurrence of biological markers (sesqui and diterpenoids) within the sediments (coaly shales), coals and jet samples indicates the origin of terrestrial organic matter from conifers. Biomarker composition of jet samples indicates enhanced aromatisation of sesqui and diterpenoids. These results correspond to enhanced aromatisation of steranes, as reflected by generally higher relative contents of triaromatic steroids in the jet. Because of comparable maturation (0.5–0.6% R r ) of the coals, coaly shales and the jet samples, confirmed by the isomerisation of αβ C 31 -hopanes and ααα C 29 -steranes, the increase in aromatisation in the jet is thought to reflect increased contribution of bacteria to organic matter degradation. The lack of enrichment of the jet samples in hopanes relative to steranes suggests that enhanced biomarker aromatisation is caused by anaerobic rather than by aerobic bacteria.

The type section of the Maikop Group (Oligocene-Lower Miocene) at the Belaya River (North Caucasus): Depositional environment and hydrocarbon potential

The type section of the Oligocene to lower Miocene Maikop Group, considered the main source rock in the eastern Paratethys, has been studied using geochemical proxies to gain insights into depositional setting and hydrocarbon potential. The Maikop Group at the type section is approximately 600 m (2000 ft) thick. Deposition commenced after a major late Eocene sea level drop and a subsequent early Oligocene sea level rise. The Maikop Group is composed mainly of carbonate-free pelitic rocks. Calcareous rocks are limited to the lower Oligocene succession, including the Polbian Bed that forms a basin-wide marker horizon deposited during a time with significantly decreased salinity (Solenovian event). Anoxic conditions prevailed and were only interrupted for longer periods during deposition of the lower part of the lower Oligocene Pshekha Formation, the Polbian Bed, and the lower Miocene Olginskaya Formation. Total organic carbon (TOC) contents range up to 3.5 wt. %. Hydrogen index values are typically less than 300 mg hydrocarbons (HC)/g TOC but reach 420 mg HC/g TOC in black shales overlying the Polbian Bed (lower Morozkina Balka Formation). Organic richness of this level, approximately 10 m (33 ft) thick, is controlled by low salinity and high bioproductivity. The Maikop Group could generate approximately 2.0 t HC/m2 surface area. A significant part (0.45 t/m2) comes from the lower Morozkina Balka Formation, which generates a high-wax paraffinic–naphthenic–aromatic mixed oil. The Pshekha, upper Morozkina Balka, and Batalpashinsk Formations would generate low-wax oil or condensate. The hydrocarbon generation potential of the overlying formations is minor. Overall, the generation potential of the Maikop Group is surprisingly low.

Depositional environment and source potential of Jurassic coal-bearing sediments (Gresten Formation, Höflein gas/condensate field, Austria)

Coal-bearing Jurassic sediments (Gresten Formation; Lower Quartzarenite Member) are discussed as source rocks for gas and minor oil in the basement of the Alpine–Carpathian frontal zone (e.g. Höflein gas/condensate field). Core material has therefore been analysed to characterize depositional environment and source potential of the Lower Quartzarenite Member (LQM). Geochemical data from the Höflein condensate are used to establish a source–condensate correlation. The LQM was deposited in a flood basin with transitions to a delta-plain environment. Coal originated in frequently flooded mires and evolved within an oxygenated and acidic environment. It is inferred from geochemical data that organic matter from aquatic macrophytes and gymnosperms contributed to coal formation. Wildfires were abundant and oxidation of plant remains occurred frequently. This resulted in the formation of dull coal with very high inertinite contents. Bituminous shales were formed in deeper waters under dysoxic conditions. Apart from abundant algae and micro-organisms, it is concluded that there was an increased contribution of higher land plants relative to macrophytes to the biomass of the shales. Despite high inertinite contents, coal within the LQM has a significant oil potential. Bituminous shales contain a Type III–II kerogen. According to pyrolysis–gas chromatography data, coal and shale generate a high wax paraffinic oil. The organic matter is immature to marginal mature (0.55% Rr). Bituminous shales are considered a potential source for the Höflein condensate. Coal may be the source for gas and minor oil in the Klement Field, but is not the source for the condensate. The equivalent vitrinite reflectance of the condensate is 0.8%, suggesting condensate generation at 4–4.5 km depth. The Gresten Formation reaches this depth near its depocentres, implying southward-directed migration of the Höflein condensate.

Thermochemical and geochemical characteristics of sulphur coals

Abstract Gas chromatography–mass spectrometry (GC-MS) method was applied for investigation of the extracts obtained from three pairs of Donets bituminous coals (76–79% of C daf ) of similar rank but differing in sulphur content. The elemental characteristic of the coals and hydrocarbon composition of their extracts reflect the differences in the environments of sulphur coals formation and differences in their structure. The thermal and natural coalification pathways of low- and high-sulphur coals formed under low-reduced and reduced conditions during early diagenesis were determined.