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The Upper Jurassic marlstones (Mikulov Fm.) and marly limestones (Falkenstein Fm.) are the main source rocks for conventional hydrocarbons in the Vienna Basin in Austria. In addition, the Mikulov Formation has been considered a potential shale gas play. In this paper, organic geochemical, petrographical and mineralogical data from both formations in borehole Staatz 1 are used to determine the source potential and its vertical variability. Additional samples from other boreholes are used to evaluate lateral trends. Deltaic sediments (Lower Quarzarenite Member) and prodelta shales (Lower Shale Member) of the Middle Jurassic Gresten Formation have been discussed as secondary sources for hydrocarbons in the Vienna Basin area and are therefore included in the present study. The Falkenstein and Mikulov formations in Staatz 1 contain up to 2.5 wt%TOC. The organic matter is dominated by algal material. Nevertheless, HI values are relative low (<400 mgHC/gTOC), a result of organic matter degradation in a dysoxic environment. Both formations hold a fair to good petroleum potential. Because of its great thickness (∼1500 m), the source potential index of the Upper Jurrasic interval is high (7.5 tHC/m 2 ). Within the oil window, the Falkenstein and Mikulov formations will produce paraffinic-naphtenic-aromatic low wax oil with low sulfur content. Whereas vertical variations are minor, limited data from the deep overmature samples suggest that original TOC contents may have increased basinwards. Based on TOC contents (typically <2.0 wt%) and the very deep position of the maturity cut-off values for shale oil/gas production (∼4000 and 5000 m, respectively), the potential for economic recovery of unconventional petroleum is limited. The Lower Quarzarenite Member of the Middle Jurassic Gresten Formation hosts a moderate oil potential, while the Lower Shale Member is are poor source rock. [ABSTRACT FROM AUTHOR]

The Cenozoic succession in the Lower Kura Basin includes largely uniform, often carbonate-free mudstones. Because age dating of these sediments has proved difficult, the stratigraphy of the Cenozoic succession and the distribution of organic-rich strata are poorly known. A better understanding of the Cenozoic succession is not only important for petroleum-systems-analysis, but also for the understanding of the Cenozoic evolution of the Caucasus region. Therefore, bulk geochemical data (carbonate, TOC, sulphur, Rock-Eval) of 885 samples and biostratigraphic data were collected along seven outcrop profiles. This enabled the establishment of a continuous stratigraphic record from the Middle Eocene to the Late Miocene (Pontian). The study results show that potential source rocks are present in three stratigraphic units: the Middle Koun (Middle Eocene), Maikop Group (Oligo-Miocene) and Diatom Formation (Upper Miocene). The Middle Koun is about 100 m thick near the Caspian Sea and contains highly oil-prone sediments (2–24 wt% TOC; HI 300–577 mgHC/gTOC), which may generate 1.5 tHC/m2. The Maikop Group contains on average 1.8 wt% TOC, but is often gas-prone. Highly oil prone layers (2–5 wt% TOC; HI 300–450 mgHC/gTOC) are rare. Nevertheless, the Upper Maikop Formation may generate ∼2 tHC/m2. The Diatom Formation contains paper shales with high TOC contents (3–22 wt%) and HI values (350–770 mgHC/gTOC). The paper shale unit is more than 60 m thick near the Caspian Sea and can generate 3.8 tHC/m2. Previously it was thought that the Maikop Group had the highest petroleum potential, whilst Upper Miocene and Middle Eocene source intervals were overlooked. The Middle Eocene to Lower Oligocene succession in the Kura Basin is largely carbonate-free. In contrast, coeval successions elsewhere in the Caucasus region contain sediments with varying, but often high carbonate contents. Differences in carbonate content imply greater water depth during deposition in the Kura Basin. • Cenozoic organic matter-rich rocks in Azerbaijan occur in three distinct stratigraphic units. • The Middle Eocene Middle Koun Member is a prolific, but overlooked, source rock capable of generating up to 1.5 tHC/m2. • The Oligo- Miocene Maikop Group contains moderate amounts of organic matter, but can still generate about 2 tHC/m2. • Upper Miocene paper shales in the Diatom Fm. contain a remarkably high petroleum potential and may generate 3.8 tHC/m2. • Water depth during Middle Eocene to Lower Oligocene time was higher in Azerbaijan than in other in other Caucasus areas. [ABSTRACT FROM AUTHOR]

The Alpine–Dinaric Transition Zone in Slovenia comprises the fold and thrust belt of the Southern Alps (South Karawanken Range, Julian Alps), Slovenian Basin and the Dinarides. The Slovenian Basin located between the Julian and Dinaric carbonate platforms evolved during Middle Triassic time and remained in a deep marine setting till the Late Cretaceous. The thermal history of Carboniferous to Eocene rocks in that area was investigated using vitrinite reflectance (VR) data, apatite fission track analysis and numeric 1D basin modeling. The study shows that maturity patterns are mainly controlled by the thickness of Upper Cretaceous to Eocene flysch deposits, filling the accommodation space. Therefore the thermal overprint reaches a maximum (> 4%Rr) in Triassic to Cretaceous sediments of the Slovenian Basin and decreases towards the north and south. Minor sedimentary burial of the Adriatic Carbonate Platform and the Julian Alps results in a lower thermal overprint (< 1.5%Rr). The thickness of flysch sediments was about 5 km in the area of the Sava Folds, but significantly higher in the central part of the Slovenian Basin. Heat flow during maximum burial in Eocene time was in the order of the global average (60 mW/m 2 ). Cooling of Paleozoic and Mesozoic sediments below 110 °C occurred between Late Eocene and Early Oligocene times in different parts of the study area. Nappe stacking due to Early (Dinaric) and Late Cenozoic (Alpine) compressional tectonics did not influence the thermal maturity of the sediments. [ABSTRACT FROM AUTHOR]

The Oligocene to early Miocene fine-grained succession in the Eastern Carpathians includes, from base to top the Lower Menilite (LMM), Bituminous Marl (BMM), Lower Dysodilic Shale (LDSM), and Upper Dysodilic Shale (UDSM) members. These stratigraphic units, constituting the main hydrocarbon source rocks in the Eastern Carpathians, have been studied in an outcrop section to determine its depositional environment and hydrocarbon potential. The LMM contains high amounts of TOC, but because of low thickness its source potential is limited. The organic matter of the overlying BMM is mainly derived from autochthonous marine organisms including bacterial biomass. TOC contents are moderate because of dilution by carbonate minerals. Calcareous nannoplankton dates the BMM into nannoplankton zones NP21-22. Salinity and redox conditions varied from reduced to slightly enhanced and from strictly anoxic to dysoxic. The LDSM contains carbonate-free black shale and sandstone beds deposited in a depositional lobe under anoxic conditions. Despite of high HI values, land plants form a significant part of the organic matter. Channel fill sediments form the top of the LDSM. The lower part of the early Miocene UDSM accumulated in a lobe, whereas its upper part represents a basin plain setting. MTTC ratios reflect a trend from slightly enhanced to slightly decreased normal marine salinity. The presence of aryl-isoprenoids suggests a temporary photic zone anoxia controlled by salinity variations. Both marine and terrestrial biomass contributed to the organic matter. A major change towards oxic conditions occurred at the boundary between the UDSM and the overlying Gura Soimului Formation. The studied succession can generate 6 t of hydrocarbons per square meter. All members are oil prone, but yield oil with different biomarker characteristics. This allows the identification of oil generated from different lithostratigraphic units. [ABSTRACT FROM AUTHOR]

The Dniepr-Donets Basin (DDB) hosts a multi-source petroleum system with more than 200 oil and gas fields, mainly in Carboniferous clastic rocks. Main aim of the present study was to correlate accumulated hydrocarbons with the most important source rocks and to verify their potential to generate oil and gas. Therefore, molecular and isotopic composition as well as biomarker data obtained from 12 oil and condensate samples and 48 source rock extracts was used together with USGS data for a geological interpretation of hydrocarbon charging history. Within the central DDB, results point to a significant contribution from (Upper) Visean black shales, highly oil-prone as well as mixed oil- and gas-prone Serpukhovian rocks and minor contribution from an additional Tournaisian source. Devonian rocks, an important hydrocarbon source within the Pripyat Trough, have not been identified as a major source within the central DDB. Additional input from Bashkirian to Moscovian (?) (Shebelinka Field) as well as Tournaisian to Lower Visean rocks (e.g. Dovgal Field) with higher contents of terrestrial organic matter is indicated in the SE and NW part, respectively. Whereas oil–source correlation contradicts major hydrocarbon migration in many cases for Tournaisian to Middle Carboniferous reservoir horizons, accumulations within Upper Carboniferous to Permian reservoirs require vertical migration up to 4000 m along faults related to Devonian salt domes. 1-D thermal models indicate hydrocarbon generation during Permo-Carboniferous time. However, generation in coal-bearing Middle Carboniferous horizons in the SE part of the basin may have occurred during the Mesozoic. [ABSTRACT FROM AUTHOR]

Marine Carboniferous shales are proven hydrocarbon source rocks in central Britain. In this contribution the depositional environment and shale gas/liquid potential of the lower Namurian part of the Bowland Shale Formation is studied using 77 thermally immature samples from the Duffield borehole. The Bowland Shale Formation comprises mudstone and turibidite lithofacies reflecting a pronounced sea level controlled cyclicity. The total organic carbon (TOC) content of the mudstones lithofacies (including marine bands) and of fine-grained rocks within the turibidite lithofacies varies between 1.3 and 9.1%. Hydrogen index (HI) values imply the presence of kerogen type III-II. According to biomarker ratios and bulk geochemical parameters, marine bands (maximum flooding surfaces, mfs) were deposited in deep water with slightly enhanced, normal, or slightly reduced salinity. Mudstones of the highstand systems tract (HST) were deposited in environments with normal to reduced salinity, whereas photic zone anoxia favoured the preservation of marine organic matter during deposition of the mfs and the HST. The supply of landplant debris increased during the HST. Turbidites and their non-calcareous mudstone equivalents represent lowstand systems tracts deposited in low salinity environments. Terrestrial organic matter dominates in turbiditic sediments, marine organisms prevail in time-equivalent mudstones. Mudstone beneath marine bands represents transgressive systems tracts when normal marine conditions and photic zone anoxia were re-established. The mudstone lithofacies exhibits a very good to excellent potential to generate conventional mixed oil and gas. TOC content of fine-grained rocks in the turbidite lithofacies depends on the amount of detrital minerals supplied from the south. Moreover, their organic matter is gas-prone. High TOC contents and large thicknesses of the mudstone lithofacies show that the Bowland Shale Formation holds a significant shale gas/liquid potential in areas with appropriate maturity. A relatively low average HI and high clay contents may have negative effects on the shale gas potential. [ABSTRACT FROM AUTHOR]

Abstract: The Donets Basin is a major coal-mining district in eastern Ukraine and adjacent portions of Russia. It comprises the Donbas Foldbelt, which is the uplifted and compressionally deformed part of the Pripyat–Dniepr–Donets (PDD) Basin, and the significantly less deformed Western Donbas region. The PDD Basin is a Late Devonian rift structure located within the East European Craton. Thick coal-measures formed during the post-rift stage of the basin in Serpukhovian to Moscovian times, when about 130 seams, each with a thickness over 0.45m, have been deposited. Early Serpukhovian coal accumulated in a relatively narrow shore-zone. It is rich in inertinite and liptinite and very low in ash. Bashkirian and Moscovian coal have a significantly wider lateral extension and are generally rich in vitrinite. Bashkirian and Moscovian coal seams usually have high ash yields (12–18%) and high sulfur contents (2.5–3.5%), but these data vary significantly depending on peat facies. Coal rank ranges from subbituminous to anthracite and is mainly controlled by the depth of the seams and the heat flow during maximum (Permian) burial. Permo-Triassic thermal events locally overprinted the resulting coalification pattern. Coked coal occurs at the contact to presumed Permian sills and dikes southwest of Donetsk. Deep Permian burial was followed by major Permian and Mesozoic uplift events. The Donets Basin hosts proven reserves in the order of 60 Gt at the exploitable depth. The thickness of coal seams currently mined is in the range of 0.6 to 2.5m. Production during 2009 was 68.7Mt in the Ukrainian and 4.9Mt in the Russian part of the basin. Coal mines in the Donets Basin are among the gassiest in the world. The average methane content of coal is 14.7m³/t, but numerous seams have significantly higher gas content. The high methane content presents a severe mine safety problem. On the other hand, it represents also a high potential for coal mine bed methane projects. Emissions of coal gas released by mining and related structurally induced underground hazards (coal and gas outbursts) are a major problem for safe and efficient coal exploitation in the basin. [Copyright &y& Elsevier]

Abstract: The Oligocene Ruslar Formation is a hydrocarbon source rock in the Kamchia Depression, located in the Western Black Sea area. Depositional environment and source potential of the predominantly pelitic rocks were investigated using core and cuttings samples from four offshore wells. In these wells the Ruslar Formation is up to 500m thick. Based on lithology and well logs, the Ruslar Formation is subdivided from base to top into units I–VI. Dysoxic to anoxic conditions and mesohaline to euhaline salinities prevailed during deposition of the Ruslar Formation. Relatively high oxygen contents occurred during early Solenovian times (lower part of unit II), when brackish surface water favoured nannoplankton blooms and the deposition of bright marls (“Solenovian event”). Anoxic conditions with photic zone anoxia were established during late Oligocene times (units III and IV) and, probably, reflect a basin-wide anoxic event in the Eastern Paratethys during Kalmykian times. Organic carbon content in the Ruslar Formation is up to 3%. Autochthonous aquatic and allochthonous terrigenous biomass contribute to the organic matter. Relatively high amounts of aquatic organic matter occur in the lower part of the Ruslar Formation (units I and II) and in its upper part (unit VI). Diatoms are especially abundant in the lower part of unit VI. The kerogen is of type III and II with HI values ranging from 50 to 400mgHC/gTOC. Units I and II (Pshekian, lower Solenovian) are characterized by a fair (to good) potential to produce gas and oil, but potential sources for gas and oil also occur in the Upper Oligocene units IV–VI. [Copyright &y& Elsevier]

Abstract: More than one hundred and thirty coal seams and coaly layers occur in the Donets Basin (Donbas). Twenty-eight (52 samples) of them, ranging in age from Serpukhovian (Late Mississipian) to Gzhelian (Late Pennsylvanian), 33 clastics and three limestones were studied in terms of maceral composition, sulphur contents, and biomarker distribution. Diterpanes are used to estimate the contribution of different groups of plants and the height of the water table in the swamp; hopanes are a measure of bacterial activity in the peat; and steranes indicate the relative input of wood and algae. Stratigraphic trends in these parameters are discussed in relation to paleoenvironment, climatic changes, and eustacy. A tropical climate prevailed in the Donbas from Serpukhovian to Kasimovian times. Nevertheless, periods with drier and wetter conditions can be distinguished based on maceral and biomarker data. Relatively dry conditions are observed during Serpukhovian and Vereian times, whereas wetter climates with a maximum of coal deposition occurred during the (late) Bashkirian, most of the Moscovian, and the earliest Kasimovian. No economic coal seams are hosted in upper Kasimovian and Gzhelian deposits, a result of a change to an arid climate. Our data also suggest climatic changes during sequences of different order. For the second-order, third-order, and fourth-order sequences, relatively dry or wet conditions occurred during coal deposition in the lowstand systems tract, an intermediate climate during the transgressive systems tract and the maximum flooding, and a wet climate during the highstand systems tract. The results for high frequency sequences support the Cecil''s paleoclimatic model: an intermediate paleoclimate during LST (sandstone and levee siltstone), a wet climate during early TST (coal), and a dry climate during late TST (limestone), MFS (claystone), and HST (deltaic siltstone). Coals deposited during maximum flooding periods are more enriched in C27 steranes derived from algae, and contain lower proportions of C29 steranes derived from the wood of higher plants. [Copyright &y& Elsevier]

Abstract: An asphaltene rich, non-producible petroleum (tar) fills the pore spaces of an Eocene sandstone reservoir in the Alpine Foreland Basin near Bad Hall (Austria). Despite good reservoir properties, the solid bitumen prevents economic petroleum exploitation. Petrographical and geochemical techniques were applied in order to characterise the source rock of the bitumen and the formation mechanisms of the tar. Biomarker data argue for a marine shaly to marly source and indicate that the Schöneck Formation, the main source rock in the area, also sourced the Bad Hall Nord structure. The methylphenanthrene index implies a source rock maturity equivalent to 0.7% R r indicating a lateral migration distance in the order of 15–20km. Natural deasphalting is the predominant mechanism for the formation of the tar. Adsorption of asphaltenes onto authigenic kaolinite played a major role during deasphalting and in the fixation of asphaltenes. Gas injection and migration-related asphaltene precipitation are further feasible mechanisms. [Copyright &y& Elsevier]

Abstract: Numerous differences in the petrography and organic geochemistry of two Tertiary, low rank coal deposits of Bulgaria, formed within comparable depositional environments, are outlined. Different floral assemblages are indicated as the main sources of organic matter. For the Eocene Bourgas sub-bituminous coals a warm climate plant community dominated by angiosperms is reflected in the biomarker composition, whereas a coniferous flora was the main source of the resinous organic matter of the Miocene Maritza-East lignite. The results are in agreement with palaeobotanical data. These differences in the peat forming vegetation of the Paleogene compared to the Neogene of Bulgaria are attributed to decreasing temperature during the Tertiary. The abundance of resinous compounds relative to lipids from plant waxes (long chain n-alkanes), as well as the preservation of plant tissue, are mainly controlled by gymnosperm/angiosperm ratios. Pristane/phytane and diasterenes/sterenes ratios reflect variations in redox conditions and the pH of the depositional environments, caused by eustatic sea level changes, freshwater inflow, or varying (ground)water table. Changing Eh and pH values are associated with differences in microbial activity controlling the extent of gelification of plant tissue. Bacteria most probably contributed to the aromatisation of triterpenoids in the mire. Enhanced thermal maturation of organic matter during diagenesis is reflected in higher contents of n-alkanes and the presence of alkyl naphthalenes in the Bourgas coals. Alkyl naphthalenes are thought to have been formed from pentacyclic triterpenoids rather than from resinous compounds. [Copyright &y& Elsevier]

The Donbas Foldbelt forms part of a large Devonian rift cross-cutting the southern part of the Eastern European Craton. It comprises a 20-km-thick Devonian and Carboniferous sedimentary succession. Maximum burial occurred during early Permian time and was followed by a major exhumation phase. In this study we use zircon and apatite fission track dating to reconstruct the post-depositional thermal evolution of the inverted basin. Modelling of the fission track data, combined with modelling of vitrinite reflectance data, reveals that large parts of the basin were affected by a Permo-Triassic (∼250 Ma) heat flow event, which was presumably related to Permo-Triassic andesitic magmatism. This Permo-Triassic thermal event was predicted by previous modelling of vitrinite reflectance data, but only the fission track data indicates its wide areal distribution. Probably large parts of the southern margin of the Eastern European Craton were affected by this event. Whereas rocks west of the city of Donetsk (Krasnoarmeisk Monocline) experienced Permo-Triassic temperatures in the range of 90–105 °C, rocks northwest of Donetsk were heated to up to more than 240 °C. Jurassic temperatures northeast of Donetsk were in the order of 90–100 °C. These relatively high temperatures imply that a significant part of the Carboniferous sequence became eroded only during early Cretaceous times and/or that the Jurassic heat flow was significantly increased (∼90 mW/m2). Elevated heat flows may be related to Jurassic magmatic activity. Sediments in the southern Donbas Foldbelt (Yuzhno–Donbassky region) and the westernmost Krasnoarmeisk Monocline record cooling below 60 °C during Jurassic times, whereas samples northeast of Donetsk cooled below 60 °C during Cretaceous times. A correlation between this last cooling and the present-day depths of the samples suggests that the main episode of folding along the South Syncline and the South Anticline pre-dates Cretaceous cooling. [Copyright &y& Elsevier]

The Dniepr–Donets Basin (DDB) is a Late Devonian rift structure located within the East-European Craton. Numerical heat flow models for 13 wells calibrated with new maturity data were used to evaluate temporal and lateral heat flow variations in the northwestern part of the basin.The numerical models suggest that heat flow was relatively high during Late Carboniferous and/or Permian times. The relatively high heat flow is probably related to an Early Permian re-activation of tectonic activity. Reconstructed Early Permian heat flow values along the axial zone of the rift are about 60 mW/m2 and increase to 90 mW/m2 along the northern basin margin. These values are higher than those expected from tectonic models considering a single Late Devonian rifting phase. The calibration data are not sensitive to variations in the Devonian/Carboniferous heat flow. Therefore, the models do not allow deciding whether heat flows remained high after the Devonian rifting, or whether the reconstructed Permian heat flows represent a separate heating event.Analysis of the vitrinite reflectance data suggest that the northeastern Dniepr–Donets Basin is characterised by a low Mesozoic heat flow (30–35 mW/m2), whereas the present-day heat flow is about 45 mW/m2. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

The Carboniferous succession in the Donets Basin hosts about 130 seams, each with a thickness over 0.45 m. Nine economically important seams from the (south)western Donets Basin are studied using organic petrographical, inorganic geochemical, and organic geochemical techniques. The main aim of the study is the reconstruction of peat facies of Serpukhovian (Mississippian) and Moscovian (Middle Pennsylvanian) coals.Formation of major coal seams commenced during Serpukhovian times. Early Serpukhovian coal accumulated in a relatively narrow shore-zone and is rich in inertinite and liptinite. Very low ash yields, low to moderate sulphur contents, and upward increasing inertinite contents suggest coal deposition in raised mires.Moscovian coal has a significantly wider lateral extension and is generally rich in vitrinite. Coal properties vary widely in response to different peat facies. Low-sulphur, low-ash k7 coal was formed in a raised mire or in a low-lying mire without detrital input. l1 and l3 seams containing several fluvial partings were formed in low-lying mires. Both seams are more than 2 m thick. Seams m2 and m3 contain high-sulphur coal, a consequence of deposition in a peat with marine influence. In contrast, syngenetic sulphur content is low in the m51 upper seam, which was formed in a lacustrine setting. The late Moscovian n1 seam, up to 2.4 m thick, accumulated in a swamp with a vegetation rich in bryophytes and pteridophytes. The properties of the n1 seam are transitional between those of Serpukhovian and other Moscovian seams. Differences in maceral composition between Serpukhovian and Moscovian coals probably reflect changes in climate and vegetation type.Tuff layers are observed in the l1, l3, and m3 seams. The l3 and m3 seams contain abundant authigenic quartz. Trace element contents are high in many seams. As contents are especially high in seams c102, k7, l3 and m3. Ash in the l3 seam contains up to 8000 ppm As. Co is enriched near the base of several seams. Maxima up to 2400 ppm occur in the ash of the k7 and l3 seams. Cd contents in ash are frequently as high as 30 or 40 ppm. [Copyright &y& Elsevier]

Tectonically controlled lakes developed during Miocene lateral extrusion of the Eastern Alps. Mineralogy, and the inorganic and organic geochemistry of rocks from three boreholes were investigated to reconstruct the evolution of Lake Ingering and Lake Groisenbach and to study the distribution of source rocks in pull-apart basins. Gas-prone coal and oil-prone sapropelic shale accumulated during the initial, shallow stages of Lake Ingering. Thereafter, the lake deepened rapidly. 125-m-thick prodelta shale containing a type II kerogen was deposited in the brackish, several hundred meter deep, hydrologically closed lake. Afterwards, decreasing subsidence allowed the filling of the lake by prograding deltas. During the advance of the deltaic systems, the lake became shallower, hydrologically open, and the brackish influence terminated. Source rock quality decreased significantly during the filling stage of the lake, a consequence of dilution of autochthonous organic matter and of enhanced input of land plants. Despite its considerable dimensions, formation and filling of Lake Ingering lasted only two million years. Lake Groisenbach was considerably smaller and more susceptible to high-frequency changes in lake chemistry. Although the water body was temporarily oligosaline, brackish conditions did not occur. High sulphur contents were due to anoxic events and the inflow of Ca-rich waters. Abundant dissolved silica favoured diatoms blooms. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

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 Ko¨flach–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. [Copyright &y& Elsevier]

Organic-rich rocks (Scho¨neck Formation) from five wells representing a section across the northern paleo-slope of the Austrian Molasse Basin were studied using a multi-method approach including petrography, X-ray diffraction, organic and inorganic geochemistry, and C- and N-isotopes of the organic material. Organic matter accumulation commenced during the latest Eocene and was dependent on variations of currents, salinity, organic productivity, and nutrient supply. Initial marl deposition (and phosphorite-formation) under dysoxic conditions was followed by organic-rich mud deposition associated with benthic and photic zone anoxia. This paleoceanographic situation resembles the first isolation of the western Central Paratethys. Deposition of organic-rich rocks terminated during lower Oligocene time when changing current patterns and decreasing salinity caused a breakdown of water column stratification. Even though the Scho¨neck Formation is an excellent source rock, major differences exist in the petroleum potential of the Scho¨neck Formation deposited in upper and lower basin slope settings. The Scho¨neck Formation from the upper slope is characterised by TOC contents up to 12% and HI values between 500 and 600 mgHC/gTOC. In the lower slope settings, TOC values are generally below 2%. [Copyright &y& Elsevier]

The Donets Basin (Donbas) is one of the major late Paleozoic coal basins in the world. The Donbas Foldbelt is an inverted part of the Donets Basin characterized by WNW–ESE-trending folds and faults. The age of basin inversion is under discussion. Large parts of the Donets Basin host anthracite and meta-anthracite. Low-rank coals are restricted to the western and northern basin margins. Vitrinite reflectance patterns along the Gorlovka Anticline indicate syn-deformational coalification. Vitrinite reflectance isolines are displaced along thrusts, clear evidence that main coalification predates late faulting.1-D and 2-D numerical models were applied to elucidate the factors that control coalification in the western Donets Basin (Krasnoarmeisk Monocline, Kalmius–Torets Depression, South Syncline).The models indicate that the depth of the seams and the heat flow during maximum (Permian) burial are the most important parameters. The thickness of late Carboniferous and Permian rocks increased from the southwestern basin margin towards the basin center. Permian erosion along the Krasnoarmeisk Monocline and in the Kalmius–Torets Depression was on the order of 2–3 km. More rocks were eroded southeast of the Donetsk–Kadievka Fault Zone (4–5 km). Heat flow during maximum burial was in the range of 40–75 mW/m2. Heat flow in the Krasnoarmeisk Monocline and the Kalmius–Torets Depression increased in a northeastward direction from 40 to 55 mW/m2. Heat flow at the eastern edge of the Kalmius–Torets Depression and in the South Syncline was in the range of 60–75 mW/m2 and increased towards the southeast. The resulting coalification pattern in this area was overprinted by thermal events in the northern Krasnoarmeisk Monocline and the South Syncline. These are probably related to (Permian?) magmatic intrusions. Coked coal occurs at the contact to presumed Permian sills and dikes southwest of Donetsk. [Copyright &y& Elsevier]

The Dobrudzha Basin in northeast Bulgaria contains 86 coal seams distributed within three coal-bearing formations of Late Carboniferous age. This study presents the organic petrological and geochemical characteristics of coals from the Makedonka and Krupen Formations, containing some of the most prominent coal seams. These were characterized by means of proximate and Rock-Eval analyses, vitrinite reflectance measurements, organic petrography and GCMS analysis in order to establish variations in vegetation and depositional settings. Based on random vitrinite reflectance (avg. 0.7% R r ) and TOC contents (avg. ~ 80%, daf) the coals can be classified as low rank bituminous (high volatile B-C). Low Tmax values (avg. 430 °C) further indicate a low degree of organic matter maturity. The low to moderately high ash yields, together with the presence of shaly partings, and generally low sulfur contents are consistent with peat formation in a fluviatile sedimentary environment. Petrographic analysis reveals complex maceral composition with abundant liptinite and inertinite. The predominance of detrovitrinite and the almost complete lack of strongly gelified macerals argue for enhanced humification of the plant tissues and peat formation in relatively dry environments (above water table). The distributions of n-alkanes, diterpenoids, and steranes indicate that the organic matter originated from terrestrial vascular plants. The high pristane/phytane ratios point to peat deposition under oxic conditions. Low concentrations of hopanes argue for limited bacterial degradation of the organic matter, possibly due to low pH conditions during peatification. The presence of tetracyclic diterpanes and their aromatic counterparts is attributed to pre-gymnosperm (cordaitean) input. The existence of cordaiteans, although as minor component of the palaeovegetational communities, is further evidenced by the presence of trace amounts of aromatic arborane/fernane derivatives in almost all studied samples. The occurrence of combustion-derived PAHs in all studied samples is consistent with the abundant inertinite and indicates frequent forest fires during peat formation. [ABSTRACT FROM AUTHOR]

Molecular and stable isotope compositions were determined for forty eight gas samples taken from wells producing oil form Cretaceous and Eocene reservoirs. Gas was expelled from source rock at various maturity levels (0.6–1.2%Rr). Gas maturities based on stable carbon isotopes are in general agreement with those found in oils. Nevertheless, results revealed that most fields trap methane derived from a source which is not thermogenic. Shallow northeastern reservoirs trap methane interpreted as secondary microbial in origin. The same process is proposed here as source of methane in western deposits. Moreover, those gases are enriched in 2 H isotope suggesting different methanogenesis pathways. Fields along the southern margin of the Alpine Foreland Basin where reservoir temperature exceeds 80 °C host methane generated during primary organic matter degradation. Thus, Eocene and Lower Oligocene layers should be considered as potential source rocks. This study gives new insight to filling history of traps and revealed a more complicated geological background and hydrocarbons generation than have been assumed until now. [ABSTRACT FROM AUTHOR]

Abstract: During the Miocene numerous sedimentary basins formed on the territory of Bulgaria as a result of the extensional tectonic settings related to the post-orogenic development of the late Alpine orogen. In this study, we review the petrographic composition and biomarker assemblage of two adjacent basins in western Bulgaria, i.e. Beli Breg and Staniantsi basins. Both contain lignite formed during late Miocene (c. 6Ma). Despite similar tectonic settings and depositional environments, the lignite seams possess different petrographic and organic geochemical characteristics, reflecting differences in the peat forming palaeo-communities and facies variations. The peat-forming vegetation in Beli Breg Basin was dominated by decay resistant coniferous plants, as indicated by abundant fossil wood remains, very good tissue preservation and a biomarker assemblage dominated by diterpenoids. In contrast, Staniantsi lignite is poor in fossil wood and contains a significant amount of triterpenoid biomarkers, suggesting the predominance of angiosperm plants in the swamp. The results of the biomarker analyses are consistent with palaeobotanical and palynological data from the literature. The lignite seams in both basins formed under frequently changing Eh conditions, as indicated by the severe degradation of the non-gymnosperm tissues, the low gelification index values and the variations in pristane/phytane ratio, probably as a result of seasonal drying of the swamps and changes of the ground water table. Hopanoid contents in Beli Breg lignite are very low and are consistent with the abundance of decay-resistant vegetation. In contrast, bacterial activity was obviously higher in the Staniantsi swamp, however, resulting only in slightly enhanced gelification of plant tissues. The geochemical data suggest that the diagenetic changes of the organic matter were mainly governed by thermal degradation, rather than bacterial activity. [Copyright &y& Elsevier]

Abstract: Decay of fossil wood (gelification) collected from the middle Miocene 2nd Lusatian lignite seam at the Lubstów open cast mine (Poland) is characterised by its maceral variety, fluorescence intensity and cellulose content. Cellulose decomposition leads to lower molar H/C ratio values of the organic matter as indicated by higher total organic carbon (TOC) content of samples characterised by low cellulose content. Biochemical formation of hydrocarbons in the wood due to enhanced microbial activity is evidenced by higher hydrocarbon content in the extracts. Higher relative proportions of n-alkanes and hopanoids are observed in the hydrocarbon fractions of wood remains characterised by low cellulose yield. The results provide evidence for the formation of these compounds during biogeochemical transformation of organic matter. Hopanoid contents are considered to reflect the activity of aerobic bacteria and/or fungi. Because of enhanced perylene content in the hydrocarbon fractions from gelified wood samples, fungi are considered as the major precursor carriers of this polycyclic aromatic hydrocarbon. The results provide evidence that biomarker composition of fossil wood can be used to trace biochemical transformation processes. Chemotaxonomical classification of fossil wood fragments as gymnosperms (most probably species of the coniferales families Taxodiaceae/Cupressaceae) are based on the molecular composition of terpenoid hydrocarbons and a mean δ13C value of −24.5‰. Depletion of gelified samples in 13C as compared to ungelified wood is caused by the effect of progressive decomposition of cellulose. The data indicate that cellulose δ13C data (mean δ13C=−20.8‰) are also affected by wood decomposition and so only samples with comparable cellulose content should be used for the reconstruction of environmental changes. Inter-species as well as intra-plant variation in carbon isotope differences and of decay resistance between cellulose and lignin have to be taken into account. [Copyright &y& Elsevier]

Abstract: Samples from two coal seams of the Márkushegy underground mine (Hungary) were investigated for variations in maceral composition, petrography-based facies indicators and various geochemical parameters, using three seam profiles. Both seams originate from a topogenous mire and evolved within a peneplaned coastal area covered with eutrophic swamps. The presence of foraminifera and marine algae in the marly layers is indicative of marine ingressions. Coal facies characterisation from these parameters is combined with the results from biomarker analyses of soluble organic matter in order to reconstruct the depositional environment and to relate petrography-based indicators to the molecular composition. The contents of macerals of the liptinite group are positively correlated with soluble organic matter (SOM) yields and Hydrogen Index (HI). Consistent with maceral composition and high HI values, enhanced proportions of n-alkanes of intermediate molecular weight (n-C21–25), which are predominantly found in macrophytes, are obtained from samples of the marly shales. The final drowning of the mire is reflected by decreasing pristane/phytane ratios, due to the rise of the (ground)water table and the establishment of anaerobic conditions. The observed positive correlation between pristane/phytane ratios and inertinite percentages suggests that, at least in the Márkushegy deposit, both parameters reflect variations in redox conditions of the mire. The predominance of angiosperms in the peat-forming vegetation of the Márkushegy coal is evidenced by the high relative proportions of angiosperm-derived triterpenoids. The influence of the relative proportion of fossil wood on tissue preservation (TPI) is indicated by the positive relationship of the concentration of land plant-derived terpenoid hydrocarbons and TPI. The degree of gelification of plant tissue (GI) is governed by the microbial activity in the mire, as indicated by a negative relationship between GI and the steroids/hopanoids concentration ratios. The variation of the δ 13C values of coal is obviously governed by the relative contribution of plant lipids to the biomass. The obtained negative relationship between δ 13C of the coal and GI is explained by the effect of cellulose decomposition and microbial activity on the isotopic composition of the organic matter. [Copyright &y& Elsevier]

Abstract: Samples from two lignite seams (Lower Seam, Upper Seam) of the Lavanttal basin (Austria) and additional xylite were investigated for variations in maceral composition, petrography-based facies indicators, bulk geochemical parameters, and molecular composition of hydrocarbons. Both seams originated in a topogenous mire and evolved within a transgressive setting. The final drowning of the mire is indicated by sapropelic shales. Whereas the sapropelic shale overlying the Lower Seam was deposited in a freshwater lake, the sapropelic shale above the Upper Seam represents a brackish lake. Numerous relationships are found between petrography-based facies indicators and the geochemical composition of organic matter. The contents of macerals of the liptinite group are positively correlated with soluble organic matter (SOM) yields and hydrogen index (HI). Consistent with maceral composition and high HI values, enhanced proportions of short-chain n-alkanes, which are predominantly found in algae and microorganisms, are obtained from samples of the sapropelic shales. The final drowning of the mire is reflected by decreasing pristane/phytane ratios, due to the rise in (ground)water table and the establishment of anaerobic conditions, as well as by decreasing ratios of diasterenes/sterenes, indicating increasing pH values in the mire. The degree of gelification of plant tissue (gelification index) is governed by the microbial activity in the mire, as indicated by the hopanes concentration. The differences in floral assemblage during the formation of the Lavanttal lignite seams are reflected by major differences in tissue preservation. Preservation of plant tissue (TPI) in the Lavanttal lignite is obviously controlled by the presence/absence of decay-resistant gymnosperms in the peat-forming vegetation, and additionally influenced by the relative contribution of wood to coal formation. The results provide evidence that valuable information for coal facies characterization could be obtained by petrography-based and geochemical facies indicators. An influence of the floral assemblage (gymnosperms/angiosperms ratio) and of the contribution of algal biomass on carbon isotopic composition of the organic matter (δ 13C=−24.2 to −28.6‰) is proposed. Carbon cycling during biogeochemical decomposition of plant tissue by bacteria is suggested to affect the δ 13C values of the coal. The chemotaxonomical classification of the xylites as gymnosperm remnants, based on the molecular composition of terpenoid biomarkers, is corroborated by the carbon isotopic composition of the xylites (mean δ 13C=−24.1‰) and the extracted cellulose (mean δ 13C=−20.2‰). The higher isotopic difference of about 3.9‰ between cellulose and total organic carbon of the xylites, compared to the difference between cellulose and wood found in modern trees, is explained by the smaller effect of decomposition on δ 13C of cellulose. [Copyright &y& Elsevier]

Abstract: The Zillingdorf deposit formed during the late Miocene filling of Lake Pannon and contains Austria''s largest lignite reserves. Two lignite seams are present and developed within frequently flooded, low-lying mires in near shore environments. High sulphur contents are due to the influence of the brackish water body of Lake Pannon. During peat accumulation a transgression forced the NW–SE trending shoreline northeastwards. Differences in soluble organic matter (SOM) yield and hydrocarbon content of borehole samples and woody macrofossils are related to differences in the content and composition of free lipids of microbial origin and/or hydrocarbons derived from the biogeochemical degradation of plant tissue. Variations of pristane/phytane ratios are interpreted to reflect differences in the redox conditions of the mire. Peatification in an acidic and aerobic environment is further reflected by the predominance of aromatic over saturated hydrocarbons, the presence of an intense complex mixture in the GC traces due to biodegradation processes, high ratios for diasterenes relative to sterenes, and high concentration ratios of hopanes to hop-17(21)-ene of the respective samples. Gelification of plant tissue is governed by microbial activity, as indicated by the positive relationship between gelification index and hopanoids concentration. The composition of terpenoid biomarkers indicates the predominance of gymnosperms over angiosperms and increasing proportions of angiosperms in the peat-forming vegetation with decreasing depth in the upper seam. From the sesqui- and diterpenoids present in the lignite and fossil wood remnants, a predominant role of species of the Coniferales families Cupressaceae/Taxodiaceae are concluded. The preservation of plant tissue is governed by the presence/absence of decay-resistant gymnosperms. A general influence of the floral assemblage on the isotopic composition of organic carbon of the lignite (δ13C=−27.2 to −24.6‰) is proposed. Decomposition of plant tissue and biogeochemical carbon cycling is assumed to further affect the δ13C values of the lignite. Carbon isotope data of fossil wood remnants are consistent with their chemotaxonomical classification as gymnosperms (δ13C between −22.5‰ and −24.9‰) and angiosperms (δ13C between −25.5‰ and −26.6‰), respectively. The δ13C data of the extracted cellulose reveal clear differences between fossil wood from gymnosperms (average δ13C=−20.3‰) and angiosperms (mean δ13C=−22.9‰). The higher isotopic difference of about 3.5‰ between cellulose and fossil wood, compared to that found in modern trees, is explained by the smaller effect of 13C discrimination for cellulose when compared with wood during decomposition. [Copyright &y& Elsevier]

Abstract: Deeper water black shales, overlain by coccolith-bearing marlstones representing the incipient Paratethys (example: Early Oligocene; Austrian Molasse Basin), have sedimentary characteristics similar to those of the Holocene Black Sea since 7500 years bp. Framboid pyrite size, biomarker and C–N-isotope data additionally indicate that isolation of the Paratethys resulted in Black Sea-type characteristics during nannoplankton zone NP 23. In contrast to the estuarine circulation across the Bosphorus since 7500 years bp, marine conditions prevailed in the incipient Paratethys during NP 21/22. Nitrogen was fixed and low organic carbon accumulation rates prevailed. In both settings a vertical density water-column stratification was accompanied by photic zone anoxia, and by anaerobic methane oxidation in the Paratethys. In the Paratethys increased run off, starting in NP 22, led to estuarine circulation during NP 23. During this period cyclic blooms of calcareous nannoplankton resulted in high calcite accumulation rates which diluted the coeval clay sedimentation. Similar sedimentary features in the Black Sea and the Paratethys during the earliest Oligocene are result from opposite paleoceanographic developments, both leading to estuarine circulation patterns. In the Black Sea, permanent photic zone anoxic conditions were established 7500 years bp in response to the first invasion of saline Mediterranean waters into the former freshwater lake. In contrast, brackish surface water in the Paratethys resulted from nutrient-rich freshwater diluting the marine water body. [Copyright &y& Elsevier]

In the Trbovlje region (Slovenia), an upper Oligocene coal seam up to 30 m 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 lake, 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 angiosperms 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 (δ13C=−24.0 to −28.1‰) is proposed. Carbon cycling during biogeochemical decomposition of plant tissue by bacteria is assumed to affect the δ13C 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 (δ13C=−24.0‰) and by the δ13C value (−21.8‰) of the extracted cellulose from one macrofossil. The low cellulose content of the sample (2.7%) together with the slightly higher isotopic difference of 1.6 ‰ between cellulose and fossil wood, compared to that found in modern trees, can most probably be explained by the possible reversal in 13C discrimination for cellulose when compared with wood in highly degraded samples. [Copyright &y& Elsevier]

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 δ13C 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 (δ13C between −22.7‰ and −25.1‰) and angiosperms (δ13C between −25.5‰ and −26.6‰), respectively. The δ13C data of the extracted cellulose reveal clear differences between fossil wood from gymnosperms (average δ13C=−21.0‰) and angiosperms (mean δ13C=−23.4‰). [Copyright &y& Elsevier]

Exploration efforts around the Greater Caucasus region started towards the end of the 19th century and established a wide range of petroleum play types in various basin segments around the orogen. All these plays are associated with the flanks of the inverted thrust‐fold belt and the adjacent foreland basin systems, but display significant variation among the basin segments depending on the tectonostratigraphic units involved and the degree of exploration maturity. Whereas the same main source rocks have generated most of the hydrocarbons in all the basins (namely organic‐rich shales in the Oligocene – Lower Miocene Maykop Group and the Eocene Kuma Formation), it is primarily the trapping style, both proven and speculative, which is responsible for the broad spectrum of play types observed. Eleven play type diagrams across six main petroleum provinces of the Greater Caucasus region are presented in this paper and summarize the current exploration understanding of the existing discoveries and potential new play targets. These play cartoons offer a prospect‐scale summary of both mature producing and underexplored basin segments in a coherent visual manner, and are therefore intended to promote future exploration efforts in the Caucasus region. The testing of new play types requires the proper risking of the two most critical elements in the region: hydrocarbon kitchen effectiveness, and post‐charge trap modification. The de‐risking of these factors will require properly designed, fit‐for‐purpose acquisition of modern geological and geophysical data sets. [ABSTRACT FROM AUTHOR]

Second Miocene Seam Complex (2nd MFK; germ.: 2. Miozäner Flözkomplex) holds many in-situ, not permineralised fossil tree stumps and trunks with high-cellulose contents. The state of preservation of a set of in-situ fossil trees (Taxodioxylon cryptomerioides , Sciadopityoxylon wettsteinii , and Quasisequoioxylon piskowitzense) collected from three open-cast mines (Welzow-Süd, Meuro, and Piskowitz) in Lusatia lignite mining district, Federal Republic of Germany was investigated using a multi-method research schema. Examination of preservation state of thermally immature fossil woods revealed: (1) well-preserved (non-deformed, non-degraded, and non-flattened) textinite, (2) a retained structural integrity represented by multilayered (multi-zoned) cells with primary, secondary cell wall, and middle lamella, (3) microfracturing restricted to secondary walls only, (4) preservation of polyphenolic parenchyma cells (PP cells), (5) excellent preservation of pits in ray tracheids, (6) presence of amorphous silica (opal-A) coating, and (7) crystalline silica (opal-CT) fillings of small-bladed crystals. Thermogravimetric analysis results showed dissimilar gelification status of fossil samples, supporting chlorite holocellulose assay results. The latter indicated anomalously high-cellulose values (15.6–37.6% holocellulose). The micro-FTIR data obtained revealed an excellent preservation of both hemicellulose (bands at 1740 and 1245 cm−1) and cellulose (bands at 1110 and 1040 cm−1). Micro-FTIR spectrometry indicated lack of preferential hydrolytic removal of polysaccharides in examined samples. Biomarker patterns in lignite revealed forested and prevailing reed-mire vegetation. The results indicated lower contribution of Cupressaceae and emergent macrophyta to precursor organic matter of Welzow-Süd in comparison to Piskowitz lignite. Piskowitz lignite formed in permanent mire with stable water table under reducing, mesotrophic conditions. In contrast, more pronounced water level fluctuations (reducing to slightly oxic settings) and/or post-depositional events are postulated for Welzow-Süd samples. Biomarker assemblages obtained from fossil wood show a distinct dominance of diterpenoids and δ13C values (−24.6 ‰ to −20.3 ‰) that clearly confirm gymnosperm sources. Distributions of diteprenoids and sesquiterpenoids, as well as fatty acids indicate the higher amount of saturated diterpenoids (pimarane, abietane) in fossil than in modern wood. This indicates reducing conditions promoting hydrogenation reactions. In addition to low Eh, preservation of cellulose in fossil wood was also favored by acidic conditions, very low degrees of aerobic fungal degradation, and protection of wood by Cupressaceae-derived resins. While δ13C values of fossil wood are generally consistent with stratigraphic trends and chemotaxonomical classification, slightly elevated δ13C values recorded in T. cryptomerioides and S. wettsteinii in Welzow-Süd and Meuro open-cast mines, respectively, compared to published δ13C data of fossil gymnosperm wood are also indicative for good cellulose preservation. Both preservation of in-situ Miocene fossil stumps and trunks and retention of high-cellulose contents are suggested to be related to high-amplitude temporal fluctuations associated with repeated eustatically-controlled wet-dry cycling inducing: (1) weathering of tuff- and rhyolite-dominated acidic volcanics and Lausitz granodiorite, (2) associated erosion of saprolites, and (3) peat-sourced circulation of humic acid- and fulvic acid-rich waters. The latter led to the formation of Middle Miocene kaolinite deposits, as well as to the release of silicic acid and its subsequent precipitation in form of opal-A. The latter influenced preservation of high-cellulose contents in fossil wood. • High-cellulose contents of Miocene in-situ, not permineralised fossil tree stumps and trunks in M-facies (Marcoduria -facies) • Polarised transmitted-light, calcofluor-stained CLSM, and micro-FTIR can be valuable tools to detect cellulose in non-mineralised fossil tree stumps and trunks. • Distribution of diterpenoids and sesquiterpenoids, as well as fatty acids indicate reducing conditions promoting hydrogenation reactions. [ABSTRACT FROM AUTHOR]

The Vienna Basin is a major hydrocarbon province with a long exploration history. Within the basin, secondary migration from Upper Jurassic source rocks into stacked Middle Miocene (Badenian) sandstone reservoirs was formerly considered to have occurred almost entirely along major fault zones. However recent exploration data has suggested that in areas where no major faults are present, oil may have migrated vertically through the sandy mudstone intervals separating individual reservoir units, which are therefore imperfectly sealed. In order to investigate possible secondary migration through the semi‐permeable mudstones, this study links variations in gross depositional environment (GDE) to variations in mudstone properties (e.g. mineralogy and pore size distribution). The study focussed on the mudstones which seal reservoir sandstones referred to locally as the "8.TH" and "16.TH" units. The bulk mineralogical composition of 56 mudstone and sandy mudstone (and minor intercalated muddy sandstone) samples from seal layers in 22 wells was studied by X‐ray diffraction analysis, broad ion beam – scanning electron microscopy (BIB‐SEM), mercury intrusion porosimetry (MICP) and N2 adsorption. These data are interpreted in the context of GDE maps of the Vienna Basin which were previously established using seismic and well log data. Results indicate that the gross depositional environment strongly controlled the pore space characteristics of the mudstones. The sandy mudstones in the NW part of the study area were influenced by a complex eastward‐prograding deltaic system which deposited coarse detritus into a major palaeo depression ("Zistersdorf Depression") located in the centre of the basin. Higher overall porosity and a dominance of larger pore size classes, probably resulting in reduced seal quality, were observed for sandy mudstones from well locations within feeder channels and also from within the Zistersdorf Depression. Similarly, sandy mudstones from locations associated with the long‐term input of coarser sediments in shoreline, coastal and proximal offshore settings in the NW and central parts of the study area are considered to be of lower sealing quality compared to fine‐grained mudstones deposited in distal, open‐marine settings which prevailed in the SE part of the study area throughout the Middle Miocene. In general, pore geometries were influenced by mineralogical composition; quartz‐ and detrital carbonate‐rich samples show equidimensional pores, while more elongated pores (with a higher average aspect ratio) characterize clay‐rich samples. Furthermore, matrix mesopores (2‐50 nm) determined by N2 sorption are more abundant in clay‐rich versus quartz‐rich samples, and show a pronounced positive trend with increasing percentage of illite‐smectite mixed‐layer clay minerals. This study shows that regional‐scale mudstone seals in the Vienna Basin have been influenced by variations in sedimentation associated with lateral variations in gross depositional environment during the Middle Miocene. The observed pore characteristics will serve as input data for future models of secondary migration. [ABSTRACT FROM AUTHOR]

Abstract The presence of solid bitumen strongly affects hydrocarbon storage and expulsion from a source rock as it might either cause blockage of pore throats leading to lower effective gas permeability, or contribute to hydrocarbon storage and provide migration pathways when a continuous network of hydrocarbon-wet organic matter (OM) pores is formed. Furthermore, organic matter transformation reactions are suggested to influence mineral diagenesis as well. In an attempt to characterize different solid bitumen types and transformation stages over a broad maturity interval (0.5–2.7%Ro) and for varying primary kerogen compositions, we reviewed optical and scanning electron microscopy (SEM) data of 35 solid bitumen-rich shale samples with a Cambrian to Triassic age. We were able to identify in-situ pre-oil solid bitumen, as well as remobilized post-oil solid bitumen at various maturity stages from the early oil window onwards. Solid bitumen is the main host for SEM-visible organic matter porosity; onset of porosity development in solid bitumen differs considerably between predominantly oil-prone (e.g., alginites, amorphous OM from algal and bacterial precursors) and gas-prone (vitrinite-rich) kerogen compositions. Furthermore, solid bitumen (pyrobitumen) in rocks with a terrestrially dominated OM composition seems to be considerably less mobile within the source rock compared to pre- and post-oil solid bitumen in oil-prone rocks, and less reactive in terms of porosity generation. In most samples, several solid bitumen populations with varying fluorescence properties and bitumen reflectance were observed, complicating the use of these petrographic maturity indicators. The apparently different solid bitumen populations often form continuous networks at the SEM-scale. Microstructural features such as irregularly distributed sponge-like porosity or detrital and authigenic mineral inclusions in the sub-micrometer scale were found to have a great influence on texture and reflectance under reflected light microscopy. The formation of authigenic minerals (quartz, various carbonate phases with different Ca/Mg/Fe proportions, magnetite in Cambrian samples) was observed frequently in post-oil solid bitumen of oil-prone rocks, indicating a close genetic relationship between transformation products formed during hydrocarbon generation (e.g., acetate, carbon dioxide and methane) and the dissolution and precipitation of minerals during diagenesis. In some cases, stylolite-like features in the sub-micrometer scale were found, showing that processes well-known from reservoir characterization at core-scale also play a role at the micrometer-scale. Furthermore, the observed strong interaction between organic matter transformation and mineral authigenesis indicates a substantial aqueous component even in pores filled apparently exclusively with solid bitumen. Highlights • Combined optical and scanning electron microscopy was applied to 35 Cambrian to Triassic solid bitumen-rich shales. • Solid bitumen shows complex textural features at microscale. • A pore evolution model was established for oil- and gas-prone organofacies. • Solid bitumen reflectance varies considerably within one sample. • Mineral authigenesis is strongly influenced by solid bitumen transformation. [ABSTRACT FROM AUTHOR]

During the Eocene-Oligocene transition (EOT), a major palaeoenvironmental change took place in the Paratethys Sea of central Eurasia. Restricted connectivity and increased stratification resulted in wide-spread deposition of organic-rich sediments which nowadays make up important hydrocarbon source rocks. The North Alpine Foreland Basin (NAFB) was a major gateway of the Paratethys Sea to the open ocean during the Eocene, but the age of closure of this gateway is still uncertain. The Ammer section in southern Germany documents the shallowing of this connection and subsequent disappearance of marine environments in the NAFB, as reflected in its sedimentary succession of turbidites to marls (Deutenhausen to Tonmergel beds), via coastal sediments (Baustein beds) to continental conglomerates (Weißach beds). Here, we apply organic geochemistry and date the lithological transitions in the Ammer section using integrated stratigraphy, including magnetostratigraphy and biostratigraphy. Nannoplankton and dinocyst results can be reconciled when dinoflagellate species Wetzeliella symmetrica is of late Eocene age. Our magnetostratigraphy then records C13r-C13n-C12r and allows calculation of sediment accumulation rates and estimation of ages of lithological transitions. We show that the shallowing from turbiditic slope deposits (Deutenhausen beds) to shelf sediments (Tonmergel beds) coincides with the Eocene-Oligocene boundary at 33.9 Ma. The transition to continental sediments is dated at ca. 33.15 Ma, significantly older than suggested by previous studies. We conclude that the transition from marine to continental sediments drastically reduced the marine connection through the western part of the NAFB and influenced the oxygen conditions of the Paratethys Sea. [ABSTRACT FROM AUTHOR]

Twenty-seven oil samples from Cretaceous, Eocene and Rupelian reservoir rocks in the Alpine Foreland Basin (Austria) were analysed to evaluate the composition of diamondoid hydrocarbons using gas chromatography - triple quadrupole mass spectrometry. The oils were generated from marly and shaly Oligocene source rocks buried beneath the nappes of the Alpine foldbelt to the south of the study area. Diamondoid hydrocarbons were detected in the saturated fraction of all the analysed oils. A biodegraded oil sample from a shallow reservoir in the NE part of the study area showed an enrichment in diamondoids due to the molecule's high resistance to microbial degradation. Variations in the organic matter type of the source rock facies and differences in maturity are known to influence the composition of diamondoids. However in this study, biomarker-derived maturity parameters do not show a convincing correlation with diamondoid maturity parameters. Moreover, no cracking trend based on biomarkers and diamondoid concentrations was observed. The results indicate that the composition of diamondoids in oils from the Austrian part of the Alpine Foreland Basin is mainly controlled by heterogeneities in the Lower Oligocene source rocks, including the occurrence of a redeposited source rock succession in the western part of the study area. By contrast, EAI-1 (the ethyladamantane index) shows a good correlation with various maturity parameters and seems to be independent of source rock facies. [ABSTRACT FROM AUTHOR]

Diagenesis is an essential tool to reconstruct the development of reservoir rocks. Diagenetic processes - precipitation and dissolution - have an influence on pore space. The present paper aims to study the diagenetic history of deep-marine sandstones of the Austrian Alpine Foreland Basin. To reach that goal, sediment petrology and diagenetic features of more than 110 sandstone samples from water- and gas-bearing sections from gas fields within the Oligocene-Miocene Puchkirchen Group and Hall Formation has been investigated. Special emphasis was put on samples in the vicinity of the gas-water contact (GWC). The sediment petrography of sandstones of Puchkirchen Group and Hall Formation is similar; hence their diagenesis proceeded the same way. In fact, primary mineralogy was controlled by paleo-geography with increasing transport distance and diverse detrital input. Sediment petrographically, investigated sandstones from the water-bearing horizon seemed quite comparable to the gas-bearing sediments. In general, they can be classified as feldspatic litharenites to litharenites and display porosities of up to 30% and permeabilities of up to 1300 mD. The carbon and oxygen isotopic composition of bulk carbonate cements from these sandstones range from−3.8 to +2.2 and from −7.5 to +0.2‰ [VPDB]. However, near the Gas-Water Contact (GWC) a horizon with low porosities (<3%) and permeabilities (<0.1 mD) is present. This zone is completely cemented with calcite, which has a blocky/homogenous morphology. A slight, but significant negative shift in δ18O isotopy (−2.5‰) is evident. During early diagenesis the first carbonate generations formed. First a fibrous calcite and afterwards a micritic calcite precipitated. Further siliciclastic minerals, such as quartz and feldspar (K-feldspar and minor plagioclase), exhibit corroded grains. Occasionally, clay minerals (illite; smectite, chlorite) formed as rims around detrital grains. Late diagenesis is indicated by the formation of a low permeable zone at the GWC. [ABSTRACT FROM AUTHOR]

The Ukrainian Donets Basin (Donbas) is one of the major coal mining provinces worldwide. While the depositional setting of Donbas coals is well-studied, information on modes of trace element occurrence and changes in element composition with increasing maturation is lacking. Within the frame of the present study, both major (light) elements (C, O, S) and trace elements (e.g. As, Cu, Hg, Mo, Pb) were investigated using the electron microprobe (EPMA), which allows in-situ determination of the chemical composition of a maceral or mineral phase. Deviating maturity trends in C, O and S contents were found for different maceral groups. In relatively immature samples (< 0.7%Rr), S contents are generally higher in liptinite than in vitrinite and inertinite macerals. In liptinites and vitrinites, S contents decrease with increasing coalification, whereas S contents in inertinites remain constantly low. In mature samples (> 0.9%Rr), S contents of vitrinites and liptinites are comparable, but lower in inertinite macerals. Vitrinites in a marine-influenced coal host a higher amount of organic S, whereas the trace element concentrations are lower than in the investigated non-marine coals. As expected, a trend of increasing C and decreasing O contents was observed for vitrinite macerals within a maturity range from 0.5 to 1.4%Rr, referred to a decrease in volatile compounds during thermal maturation. The light element composition generally tends to higher homogenity with increasing coal rank. Highly variable trace element concentrations of ash residues were determined for Donbas coals, with measured As contents up to several thousand ppm. Despite enrichment in epigenetic pyrite, a clearly isolated inorganic source could not be identified, suggesting that trace element storage in macerals is an important factor. EPMA measurements revealed an organic matter affinity for at least part of the investigated elements (e.g. Hg, Mo, Pb). [ABSTRACT FROM AUTHOR]

Upper Visean Rudov Beds (V-23) are considered as one of the main source rocks within the northwestern Dniepr Donets Basin (DDB). Average TOC values within the Srebnen Bay (northwestern DDB) exceed 4% (thickness up to 100 m). Average TOC contents north and northwest of the Srebnen Bay (up to 60 m) are significantly lower (2–4%) but still sufficient for unconventional hydrocarbon production, whereas wells along the northeastern basin margin do not hold a shale oil/gas potential (<2% TOC). Insufficient information is available from positions along the basin axis in the central DDB, mainly because of considerable burial depths >5.5 km. Although hydrogen index (HI) values of the most immature samples are ≤300 mgHC/gTOC, basinal Rudov Beds host a potential to generate Paraffinic-Naphthenic-Aromatic (P-N-A) low wax oil according to pyrolysis experiments. A basinward maturity trend is visible, but the maturity cut-offs for shale oil/gas production (>0.8%Rr/>1.2%Rr) are reached at great depths (>4.5 km/5.5 km) only. Furthermore, results of kinetic experiments do not argue for presence of type IIS kerogen potentially triggering earlier hydrocarbon generation. The mineralogy of Rudov Beds varies strongly in lateral and vertical directions, limiting the predictability of mechanical behaviour. Samples from the siliceous (basinal) facies partly contain more than 60% of brittle minerals (quartz, feldspar, carbonates, etc.) suggesting a good fraccability. This value is rarely reached by samples from the transitional and lagoonal (calcareous and clayey) facies. The clay mineral fraction within many investigated Rudov samples is dominated by kaolinite, which is suggested to diminish the fraccability of shales. Apart from that, expandable clay minerals (ECM) are present in samples from more than 5 km depth, a result of low Mesozoic heat flow. [ABSTRACT FROM AUTHOR]

The Bächental bituminous marls (Bächentaler Bitumenmergel) belonging to the Sachrang Member of the Lower Jurassic Middle Allgäu Formation were investigated using a multidisciplinary approach to determine environmental controls on the formation of organic-rich deposits in a semi-restricted basin of the NW Tethys during the Early Jurassic. The marls are subdivided into three units on the basis of mineralogical composition, source-rock parameters, redox conditions, salinity variations, and diagenetic processes. Redox proxies (e.g., pristane/phytane ratio; aryl isoprenoids; bioturbation; ternary plot of iron, total organic carbon, and sulphur) indicate varying suboxic to euxinic conditions during deposition of the Bächental section. Redox variations were mainly controlled by sea-level fluctuations with the tectonically complex bathymetry of the Bächental basin determining watermass exchange with the Tethys Ocean. Accordingly, strongest anoxia and highest total organic carbon content (up to 13%) occur in the middle part of the profile (upper tenuicostatum and lower falciferum zones), coincident with an increase in surface-water productivity during a period of relative sea-level lowstand that induced salinity stratification in a stagnant basin setting. This level corresponds to the time interval of the lower Toarcian oceanic anoxic event (T-OAE). However, the absence of the widely observed lower Toarcian negative carbon isotope excursion in the study section questions its unrestricted use as a global chemostratigraphic marker. Stratigraphic correlation of the thermally immature Bächental bituminous marls with the Posidonia Shale of SW Germany on the basis of C 27 /C 29 sterane ratio profiles and ammonite data suggests that deposition of organic matter-rich sediments in isolated basins in the Alpine realm commenced earlier (late Pliensbachian margaritatus Zone) than in regionally proximal epicontinental seas (early Toarcian tenuicostatum Zone). The late Pliensbachian onset of reducing conditions in the Bächental basin coincided with an influx of volcaniclastic detritus that was possibly connected to complex rifting processes of the Alpine Tethys and with a globally observed eruption-induced extinction event. The level of maximum organic matter accumulation in the Bächental basin corresponds to the main eruptive phase of the Karoo-Ferrar large igneous province (LIP), confirming its massive impact on global climate and oceanic conditions during the Early Jurassic. The Bächental marl succession is thus a record of the complex interaction of global (i.e., LIP) and local (e.g., redox and salinity variations, basin morphology) factors that caused reducing conditions and organic matter enrichment in the Bächental basin. These developments resulted in highly inhomogeneous environmental conditions in semi-restricted basins of the NW Tethyan domain during late Pliensbachian and early Toarcian time. [ABSTRACT FROM AUTHOR]

Abstract: Hydrocarbon source rocks (i.e. Tard Clay Formation), containing type-II organic matter, were deposited in the Hungarian Paleogene Basin during Lower Oligocene. A major contribution of aquatic organisms (green algae, dinoflagellates, Chrysophyte algae) and minor inputs from macrophytes and land plants to organic matter accumulation is indicated by n-alkane distribution patterns, composition of steroids, and δ13C of hydrocarbon biomarkers. Microbial communities included heterotrophic bacteria, cyanobacteria, chemoautotrophic bacteria, as well as green sulphur bacteria. The presence of methanotrophic bacteria is indicated by 13C-depleted hop-17(21)-ene. Higher inputs of terrestrial organic matter occurred during deposition of the lower and uppermost units of the Tard Clay Formation. The terpenoid hydrocarbon composition argues for angiosperm-dominated vegetation in the area of the Hungarian Paleogene Basin. Diterpenoid hydrocarbons, derived from the resins of conifers, are about 2–3‰ enriched in 13C compared to the angiosperm biomarkers. Environmental conditions changed from marine to brackish, accompanied by oxygen-depletion in the lower parts of the water column. Organic carbon accumulation during this period was a consequence of stagnant bottom water conditions in the Hungarian Paleogene Basin due to salinity stratification. This is indicated by low pristane/phytane ratios (varying from 0.27 to 1.44), enhanced ratios of dimethylated versus trimethylated MTTCs (0.14–0.59), and the presence of aryl isoprenoids (from 0.4 to 14.1 μg/g TOC). A major marine incursion is evidenced by stable isotope ratios of organic matter and carbonates. In the uppermost member of the Tard Clay, a transition from brackish towards normal marine conditions is proposed. Up to 3 anoxic cycles are recognized in the drill core sections, separated by minima in pristane/phytane ratios and maxima in the depth trends of di-/tri-methylated MTTCs and aryl isoprenoid concentrations. In combination with the position of maxima of δ13C of carbonate and organic matter and an abrupt decrease in perylene concentrations, the cycles can be used for intra-formational correlation of the Tard Clay. [Copyright &y& Elsevier]

Abstract: The type of organic matter (OM) in European Carboniferous and Permian swamp and lake sediments from the Carboniferous and Permian was determined using organic petrography, Rock–Eval data and biomarker distributions. Coals deposited in swamps contain humic OM formed under oxic conditions. Boghead coals and black shales deposited in lakes contain a mixture of algal and humic OM formed under reducing conditions. Diterpanes and previous palaeobotanic studies constrain the species of plants living near the lacustrine shore or in the swamp during deposition, allowing the palaeoclimate to be inferred. During the Carboniferous, the climate was not always tropical wet, as some periods of dryness are evident from the sedimentology, palaeobotany and organic geochemistry. During the Permian, the climate was not always tropical dry as some periods of wetness associated with the monsoons are recorded (Roscher, M., Schneider, J.W., 2006. Permocarboniferous climate: Early Pennsylvanian to Late Permian climate development of central Europe in a regional and global context. In: Lucas, S.G., Cassini, G., Schneider, J.W. (Eds.), Non-Marine Permian Chronology and Correlation, vol. 265. The Geological Society of London, pp. 95–136). The appearance of xerophyte plants from the Stephanian was also recorded by way of aromatic hydrocarbons, retene for gymnosperms and arborane/fernane for cordaites and probably seed ferns. Cycles of wetness and dryness for Europe during the Carboniferous and Permian are proposed on the basis of comparison of aliphatic and aromatic hydrocarbons. δD values provided information on the palaeotemperature of the air in the swamps and water in lakes, as well as palaeoclimate. Values of ca. −100‰ seen in the Carboniferous coals and Permian limnic deposits are indicative of a tropical climate, in contrast to a glacial or temperate climate, where the values are ca. −200‰. The value for Carboniferous coals could result from high evapotranspiration of plants living under a wet tropical climate vs. a temperate climate. During the Early Permian the climate was dry tropical. For such samples, the δD values for the n-alkanes derived from lacustrine algae were depleted in D relative to the values for the n-alkanes derived from terrestrial higher plants, attributed to the higher evapotranspiration on land than evaporation from the lake. Alternatively, the xerophytic plants that drifted into the lake via a river could have grown during a dry phase and the autochthonous algae bloomed during a wet phase. [Copyright &y& Elsevier]

Abstract: The main purpose of this contribution is to estimate methane production and to define its migration paths and storage in the Donets Basin formations for exploitation of methane and forecast of mining hazards. In order to study methane migration and storage, maps of production calculated by 2D modelling, adsorption capacity of methane in coal, and present-day methane contents were constructed for an altitude of −300 m (close to 500 m depth) in this basin. The results show that three principal factors influenced the methane migration and accumulation in Donets Basin: 1) faults that acted as migration pathways, 2) a replacement of thermogenic methane by endogenic CO2 in the central and SE parts, and 3) the occurrence of magmatic events in some areas in this basin. Finally, in Donbas, the areas with the highest methane potential and the maximum risk of outburst are not the areas with anthracite that produce the highest volume of methane, but areas with volatile bituminous coals where an impermeable cover preserved the accumulated gas until the Cenozoic and where dextral shear belts facilitated its migration. [Copyright &y& Elsevier]

Abstract: The main purpose of this contribution is to compare the ability of Carboniferous coals from the Donets Basin of the Ukraine and Cretaceous coal from the Sabinas Basin of the Mexico to generate hydrocarbon gases (C1–C5). Two bituminous coals from the Donets Basin (2c10YD and 1l1Dim; 0.55 and 0.65%R r respectively) and one bituminous coal from the Sabinas Basin (Olmos, 0.92%R r) were studied using heating experiments in a confined-pyrolysis system. The highest rank reached during the heating experiments corresponds to the anthracite stage (2.78 and 2.57%R r) for the 2c10YD and 1l1Dim coals and (2.65%R r) for the Olmos coal. The composition of the generated (C1–C5) gases was evaluated using a thermodesorption-multidimensional gas chromatography. The results show that the Carboniferous Donets coals produced more wet gas and methane during pyrolysis than the Cretaceous Olmos coal. This is probably due to their higher liptinite (6–20%) and collodetrinite content and to the loss of a major part of the petroleum potential of the Olmos coal during natural coalification. C2–C5 compounds are mainly derived from the cracking of liquid hydrocarbons. Ethane is the most stable compound and formed from the cracking of higher hydrocarbon component. Large amounts of methane (up to 81 mg/g coal for the Donets coals and 50 mg/g coal for the Sabinas coal) were formed at high temperatures by cracking of previously formed heavier hydrocarbons and by dealkylation of the coal matrix. A linear relationship was observed between methane generation and the maturity level of both coal types. [Copyright &y& Elsevier]

Abstract: Organic-rich samples from the Holocene sedimentary sequence of Lake Sarbsko were investigated to reconstruct variations in the aquatic system in response to environmental change. The aims were to (i) identify organic matter (OM) sources, (ii) examine changes in soluble OM composition in relation to fluctuations in limnological conditions and (iii) validate the sensitivity of organic geochemical indicators in tracing environmental changes. Diatom frustules are abundant in all samples. Alginite macerals and terrigenous organic matter further contribute to the sedimentary OM. Organic petrography, total organic carbon (TOC)/N ratio values and high content of biogenic silica (SiO2biogenic) argue for a predominant algal source of OM. In contrast, the n-alkane distributions, high relative abundance of C29 steroid hydrocarbons and high content of detrital quartz in the sediments provide evidence for the input of terrigenous material as a major OM source within the basin. The terpenoid biomarker composition indicates a contribution from conifers and angiosperms. From the diterpenoids in the samples a contribution from species of the coniferales family Pinaceae is concluded. TOC/S and Mg/Ca values, as well as steroid/hopanoid concentration ratios, reflect enhanced water salinity in this coastal lake due to ingression of brackish water from the Baltic Sea during the Atlantic and Sub-Atlantic periods. As indicated by the positive relationship between δ 13C of TOC and Mg/Ca, δ 13C values are influenced by changing contribution of marine vs. freshwater phytoplankton. Additional isotopic heterogeneity in δ 13C may result from differences in terrigenous OM supply vs. autochthonous OM production in the lake. The isotopic composition of calcites supports the establishment of freshwater conditions in the lake during the Sub-Boreal period. Pristane/phytane and Fe/Mn ratios are interpreted to reflect differences in the redox conditions. Oxygenation of bottom waters was temporarily variable, with highest levels of oxygen availability during the Sub-Boreal (freshwater lake). High contents of hopanoid hydrocarbons argue for enhanced microbial activity in the water column and sediment. The occurrence of 2β-methyl-hopanes is related to the presence of cyanobacteria or methylotrophic bacteria. The results demonstrate that in coastal basins of the Baltic Sea sedimentary OM content and composition are a function of the degree of isolation from the sea water. Therefore, organic geochemical data of coastal lake and lagoonal sediments are sensitive indicators for tracing environmental changes during the Holocene. [Copyright &y& Elsevier]

Nanoindentation is a valuable tool, which enables insights into the material properties of natural, highly inhomogeneous composite materials such as shales and organic matter-rich rocks. However, the inherent complexity of these rocks and its constituents complicates the extraction of representative material parameters such as the reduced elastic modulus (E r) and hardness (H) for organic matter (OM) via nanoindentation. The present study aims to extract the representative H and E r values for OM within an over-mature sample set (1.33–2.23%Rr) from the Chinese Songliao Basin and evaluate influencing factors of the resulting parameters. This was realized by means of high-speed nanoindentation mapping in combination with comprehensive optical and high resolution-imaging methods. The average E r and H values for the different particles range from 3.86 ± 0.17 to 7.52 ± 3.80 GPa and from 0.36 ± 0.02 to 0.64 ± 0.09 GPa, respectively. The results were subsequently processed by the unsupervised machine learning algorithm k -means clustering in order to evaluate representative E r and H results. The post-processing suggests that inherent heterogeneity of OM is responsible for considerable data scattering. In fact, surrounding, underlying and inherent mineral matter lead to confinement effects and enhanced E r values, whereas cracks and pores are responsible for a lowered stiffness. Adjusted for these influencing factors, a declining trend with increasing maturity (up to 1.96%Rr) could be observed for E r , with average values calculated from representative clusters ranging from 5.88 ± 0.37 down to 4.07 ± 0.32 GPa. E r slightly increases again between 2.00 and 2.23%Rr (up to 4.85 ± 0.35 GPa). No clear relationship of H with thermal maturity was observed. The enhanced accuracy archived by a large data set facilitated machine learning approach not only improves further modelling attempts but also allows insights of impacting geological processes on the material parameter and general understanding of mechanical behavior of OM in rock formations. Thus, the presented multimethod approach promotes a fast and reliable assessment of representative material parameters from organic rock constituents. • Extracting representative mechanical parameters from organic matter in rocks. • Correlative imaging facilitated by femtosecond laser-machined grid. • Data processing by means of unsupervised machine learning (k -means clustering). • Revealing various impacting factors on material behavior of organic matter. [ABSTRACT FROM AUTHOR]

Various compositional, depositional and maturity related influencing factors affect the complex pore structure of coal. To study the pore structural evolution at nanoscale, a well characterized sample set of vitrinite-rich Carboniferous coals from the Ukrainian Donets Basin, covering a maturity interval from 0.69 to 1.47%Rr, was selected. Conventional bright field transmission electron microscopy (BF TEM) and high-resolution TEM (HRTEM) imaging was used to directly determine pore size distributions, pore morphology, geometry factors and other structural features, while gas invasion techniques such as low-pressure gas adsorption (CO 2 and N 2) were used for the investigation of micro- and mesopore structural parameters. High-pressure CH 4 sorption experiments revealed changes in the methane storage capacity within the investigated maturity range, while associated structural changes of vitrinite were monitored by Raman spectroscopy. The results indicate pore occlusion in vitrinite mainly at peak oil window maturity, the sensibility of micro- and mesopore structure to thermal maturity and the importance of organic sulphur as a catalyst for kinetics of structural modification. Observed structural changes at 1.10%Rr were related to the onset of wet-gas generation. A structural control on micromechanical properties of vitrinite is indicated by the correlation between reduced elastic moduli from a previous study and average nanopore diameters obtained by HRTEM. The applied comprehensive approach improved the understanding of depositional and maturity-related processes that may affect pore evolution and resulting gas storage capacity of coals. • TEM and gas (ad)sorption results indicate pore occlusion at peak oil window. • High organic S contents enhance micropore and semi-graphite formation at ~0.7%Rr. • Onion-like carbon structures observed at 0.81%Rr. • Nanopore diameters influence micro-mechanical properties of vitrinite. [ABSTRACT FROM AUTHOR]

The Upper Jurassic Mandal Fm. of the Central Graben, Norway represents an important source rock that charged major petroleum accumulations in the North Sea, including the giant Ekofisk field. Nevertheless, exploration to date has been less successful than expected in marginal basin position such as the Cod Terrace, the Mandal High or the Søgne Basin, probably due to higher proportions of thermally stable (type III) kerogen. In an attempt to delineate changes in initial kerogen composition from later effects such as delayed expulsion of hydrocarbons, traditional organic petrography and scanning electron microscopy were combined with organic geochemical proxies and gas adsorption tests. The kerogen composition of the Mandal Fm. shows considerable variation. Samples hosting autochthonous coaly layers were found in wells from the Søgne Basin and the Cod Terrace, for which less generative potential was previously postulated. Nevertheless, samples hosting mainly vitrodetrinite were also found in basinal wells. A correlation of total organic carbon contents with liptinite percentages highlights enhanced bioproductivity or preservation efficiency for samples with abundant algal organic matter, that were likely deposited under deeper water and possibly oxygen-depleted conditions. By combining organic geochemical proxies with nitrogen sorption data, it could be proven that in case of the Mandal Fm., the (bituminous) organic matter fraction represents the controlling factor on abundance of micro- and mesopores and hence adsorptive gas retention. The amount of bitumen extractable from the Rock-Eval S2 peak (S2 bitumen) shows a strong correlation with the total inner surface area, suggesting that small mesopores (<10–15 nm) are mainly associated with the high-molecular bituminous fraction represented by the S2 bitumen , which appears non-porous at SEM-scale. Furthermore, the total inner surface area decreases strongly with thermal maturity, documenting a change in pore characteristics of the organic matter fraction (growth of mesopores and occurrence of macropores) by advancing hydrocarbon generation. Pyrobitumen-rich Upper Visean reference samples at peak oil and early wet gas window maturity show intense sponge-like pyrobitumen-hosted porosity coinciding with a low relative proportion of S2 bitumen (high petroleum quality). Pyrobitumen is not affected by solvent extraction, thus not contributing high-molecular weight compounds to the extracted fraction. Such inert meso- to macroporous residues might contribute only relatively little to gas sorption capacity, but might represent important storage space for free gas, as well as flow pathways during expulsion. • Samples rich in vitrodetrinite are common both in marginal and basinal positions • Coaly layers were exclusively found in the Søgne and Cod areas • A trend of TOC vs. liptinite indicates enhanced bioproductivity or preservation • High-molecular weight bitumen controls micro- and mesopores • The total inner surface area decreases with thermal maturity [ABSTRACT FROM AUTHOR]