The second Pannonian Super-Basin volume focuses on the geo-energy aspects in separate sections dedicated to geothermal energy, CCUS, hydrogen and natural gas storage and critical mineral exploration. The Pannonian Basin is the hottest sedimentary basin in mainland Europe, providing a useful template for geothermal exploration and utilization projects worldwide.

The first Pannonian Superbasin volume is dedicated to the regional geology of various Neogene extensional basins surrounded by the Alps, Carpathians and Dinarides. All these subbasins developed on highly extended continental crust, providing the locus typicus for the general evolution of extensional basins developed in a back-arc basin setting.

In the Trbovlje region (Slovenia), an upper Oligocene coal seam up to 30 in thick developed in a topogenous mire and evolved within a transgressive setting. The lower ash-rich part of the seam (unit I) accumulated in a forest swamp strongly influenced by fluvial activity. Palynomorph spectra are dominated by Taxodiaceae-Cupressaceae pollen. Ash yields decrease in the middle (unit II) and upper part of the seam (unit III), indicating decreasing fluvial activity. An increase in CaO contents reflects increasing amounts of inflowing water from an alkaline take, which progressively controlled peat hydrology in units II and III. High sulfur contents in the nonmarine coal are a result of the carbonate-rich water. Abundant pollen and spores from Myricaceae and Polypodiaceae indicate that unit II represents a bush moor. During deposition of unit III, this environment was replaced by a reed moor. Sapropelic coal (unit IV) and sapropelic shale (unit V) accumulated in a relatively large lake, which was established by another water table rise.The interpreted environmental changes are confirmed by biomarker data. Pristane/phytane ratios reflect variations of the redox conditions within the mire and reach a minimum in the sapropelic unit IV. The abundances of gymnosperm- and angiosperm-derived terpenoid hydrocarbons testify the predominance of gymnosperms over angiospenns during early peat stages (unit I), and increasing proportions of angiosperms during deposition of units II and III. Highest contents of diterpenoids coincide with maxima in the preservation of plant tissue (TPI) within unit I (wet forest swamp), suggesting that TPI is partly controlled by the input of resin-rich, decay-resistant conifers. Sections of the seam characterized by advanced gelification show low steroids/hopanoids ratios. The results imply that gelification of plant tissue is related to increased microbial activity. Evidence is provided that the hopanes could be used as a measure for the activity of aerobic bacteria, whereas for the hop-17(21)-ene a microbial origin from anaerobic (iron-reducing) bacteria is assumed. A general influence of the floral assemblage and of varying contributions of algal biomass on carbon isotopic composition of the organic matter (delta(13)C = -24.0 to -28.1parts per thousand) is proposed. Carbon cycling during biogeochemical decomposition of plant tissue by bacteria is assumed to affect the delta(13)C values of the coal.Fossil wood collected from the seam is identified as derived from gymnosperms, based on the molecular composition of terpenoid hydrocarbons. This chemotaxonomical classification is corroborated by the mean carbon isotopic compositions of the fossil wood (delta(13)C = -24.0parts per thousand) and by the delta(13)C value (-21.8parts per thousand) of the extracted cellulose from one macrofossil. The low cellulose content of the sample (2.7%) together with the slightly higher isotopic difference of 1.6parts per thousand between cellulose and fossil wood, compared to that found in modem trees, can most probably be explained by the possible reversal in C-13 discrimination for cellulose when compared with wood in highly degraded samples. (C) 2003 Elsevier B.V. All rights reserved.

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.

A Pliocene lignite seam up to 160 m thick occurs in the Velenje depression in northern Slovenia. It forms part of a non-marine transgressive sequence. Petrographic data, together with ash and sulphur content of samples from two boreholes (one located in the central, and the other in the marginal part of the seam) have been used to study vertical and lateral coal facies variations.In the central part, the lignite seam overlies fluvial sediments. Facies critical macerals and petrographic indices suggest that the lower (ash rich) part of the seam (unit I) accumulated in a wet forest swamp in an alluvial plain setting. Later this environment was replaced by a dry (telmatic) forest swamp (unit IIa). According to our interpretation, a decrease in tree density in units IIb and IIc reflects a change to a bush moor. The transition from unit II to unit m is characterized by a rapid water table rise, which resulted in the establishment of a wet (limnotelmatic) forest swamp. Within unit III, the tree density decreases and the degree of gelification increases towards the top of the seam suggesting a transition to a fen type environment. Another rapid water table rise ended peat formation in the eutrophic, topogenous mire, and established open lacustrine conditions. A calcium rich environment resulted in high pH values and is responsible for high sulphur lignites (up to 4% on a dry basis). In the upper part of the seam, the pH values were controlled by the amount of the inflowing lacustrine water.Only thin, ash-rich topotelmites accumulated along the northern margin of the mire. There, the seam originated in a wet forest swamp and was separated by Limnic and fluvial sediments from other organic rich horizons. Due to its closer vicinity to the pre-Tertiary carbonates, the depositional environment was probably even more alkaline. Therefore, the lignite shows a higher degree of gelification and is even more sulphur rich (up to 5.5% on a dry basis).