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Oligocene successions in the North Alpine Foreland Basin (NAFB) and the Western Carpathians reflect Paratethys-wide paleogeographic changes, which also control their petroleum potential. Whereas these rocks have been studied in detail in both areas, the transition zone is still under-researched. In order to fill this gap, the Oligocene succession in the Waschberg Zone, comprising the Ottenthal Formation (NP21–23) and the overlying Thomasl Formation (NP23–24) has been studied using outcrop (Waldweg section) and borehole samples (Thomasl, Poysdorf) and a multidisciplinary approach. The Ottenthal Formation is subdivided from base to top into marls and shales (Ottenthal Mbr.), diatomaceous shales (Galgenberg Mbr.) and marlstones (Dynow Mbr.). Biogenic silica contents, determined using atomic absorption spectroscopy, reach 30 wt. % in the carbonate-free Galgenberg Member, but also in the Dynow Members, which is characterized by upward decreasing productivity of calcareous nannoplankton. Close lithological relations exist with the Oligocene succession in the NAFB, but diatoms are largely missing in the latter. Organic matter contents are surprisingly low in the Ottenthal and Thomasl formations in the Waldweg section, which therefore are poor hydrocarbon source rocks. In contrast, the Thomasl Formation, encountered in the Thomasl and Poysdorf boreholes, holds a fair to good hydrocarbon potential (~ 2.2–2.5 wt. % TOC; type III and type II kerogen) and may generate 1.0 to 1.6 tons of hydrocarbons/m2. Obviously TOC contents of borehole samples are significantly higher than in outcrop samples. Because of severe indications of weathering (e.g., presence of gypsum and jarosite), a detrimental effect of weathering on the samples from the Waldweg section cannot be excluded. Biomarker data suggest a nearshore depositional environment with changing oxygen-availability and salinity. Vitrinite reflectance measurements show that the investigated sections are thermally immature.

The maceral and biomarker characteristics of 4 sublithotypes of xylite-rich coal (SXCs), pale yellow, dark yellow, brown and black, originating from the Kolubara and Kostolac lignite basins were determined. Based on these results, differences in sources and changes of organic matter (OM) resulting in formation of 4 SXCs were established. Conifers (particularly Cupressaceae, Taxodiaceae and Pinacea) had a significant impact on the precursor OM of all SXCs. The contribution of gymnosperm vs. angiosperm vegetation decreased in order pale yellow SXC>dark yellow SXC>brown SXC>black SXC. The distribution of non-hopanoid triterpenoids indicates that change of SXC colour from yellow to black is associated with reduced input of angiosperm plants from the Betulacea family. Differences in hopane distribution, bitumen content, proportion of short-chain n-alkanes and degree of aromatization of di- and triterpenoids of pale yellow SXC are controlled by microbial communities which took part in the diagenetic alteration of OM. The content of total huminites increased from black to pale yellow SXC, whereas contents of total liptinite and inertinite macerals showed the opposite trend. SXCs differ according to textinite/ulminite ratio, which sharply decreased from pale yellow to black SXC, reflecting increase in gelification of woody tissue. Regarding the composition of liptinite macerals, the SXCs mostly differ according to resinite/liptodetrinite and resinite/suberinite ratios, which are higher in yellow than in brown and black SXC. This result along with values of TOC/N ratio and Carbon Preference Index indicate that the contribution of well preserved woody material, including lignin tissue vs. the impact of epicuticular waxes decreased from yellow to black SXC.

The depositional environments and hydrocarbon potential of the siliciclastic, clayey and carbonate sediments from the Middle Miocene succession in the Varna-Balchik Depression, located in the south-eastern parts of the Moesian Platform, were studied using core and outcrop samples. Based on the lithology and resistivity log the succession is subdivided from base to top into five units. Siliciclastic sedimentation prevailed in the lower parts of units I and II, whereas their upper parts are dominated by carbonate rocks. Unit III is represented by laminated clays and biodetritic limestone. Units IV and V are represented by aragonitic sediments and biomicritic limestones, correlated with the Upper Miocene Topola and Karvuna Formations, respectively. Biogenic silica in the form of diatom frustules and sponge spicules correlates subunit IIa and unit III to the lower and upper parts of the Middle Miocene Euxinograd Formation. Both (sub)units contain organic carbon contents in the order of 1 to 2 wt. % (median: 0.8 for subunit IIa; 1.3 for unit III), locally up to 4 wt. %. Based on Hydrogen Index values (HI) and alkane distribution pattern, the kerogen is mainly type II in subunit IIa (average HI= 324 mg HC/g TOC) and type III in unit III (average HI ~200 mg HC/g TOC). TOC and Rock Eval data show that subunit IIa holds a fair (to good) hydrocarbon generative potential for oil, whereas the upper 5 m of unit III holds a good (to fair) potential with the possibility to generate gas and minor oil. The rocks of both units are immature in the study area. Generally low sulphur contents are probably due to deposition in environments with reduced salinity. Normal marine conditions are suggested for unit III. Biomarker composition is typical for mixed marine and terrestrial organic matter and suggests deposition in dysoxic to anoxic environments.

Diatomites are prolific hydrocarbon source rocks in many basins worldwide. In the broader Carpathians, diagenetically altered diatomites are called menilites, and menilitic shale successions are regarded as the most prolific hydrocarbon source rocks in the region. The abandoned Sibiciu de Sus quarry, located in the Eastern Carpathian Bend Zone of Romania, provides large exposures of the upper part of the Lower Miocene Upper Menilites, composed of various diatomite lithologies, cherts, menilitic shales and quartz-rich sandstone. The sediments are highly deformed due to soft-sediment deformation and subsequent Miocene to Pliocene contractional tectonics. Twenty-two diatom-bearing samples were examined in order (a) to determine the hydrocarbon source rock potential, (b) to document the diatom assemblages and (c) to interpret the depositional environment. The hydrocarbon potential of the studied rocks is considered good to very good, with an average TOC of 3.77 wt. % (max. 9.57 wt. % TOC) and type II-III kerogen (avg. HI: 384 mg HC/g TOC). Tmax does not exceed 424 °C suggesting that the organic matter is thermally immature. Despite that, the Production Index is high (0.1-0.3), which proves the presence of migrated hydrocarbons. The source potential index (SPI) indicates that the exposed section, if mature, could generate about 1.3 t HC/m². As the diatom preservation does not enable chemical extraction of individual valves, this study describes only genus-level findings. The diatom assemblages are dominated by Aulacoseira and Actinocyclus, whereas Ellerbeckia, Paralia and Rhaphoneis are rarely observed. The diatom assemblages indicate a nearshore, brackish-water depositional setting. [ABSTRACT FROM AUTHOR]

The Oligocene Menilite Formation represents the most important hydrocarbon source rock in the Flysch Carpathians. The formation is laterally uniform across long distances but shows strong vertical heterogeneity reflecting changes in depositional environments, which control the source rock potential. In the Czech Republic, the Menilite Formation is subdivided into the Subchert Member (nannofossil zone NP22), Chert Member (upper NP22 to lower NP23), Dynów Marlstone (NP23) and Šitbořice Member (upper NP23 to lower NP25). The present study describes in detail the Bystřice nad Olší section in the Subsilesian Unit where all four members are exposed including the uppermost part of the underlying Frýdlant Formation (Sheshory Marls). The present Frýdlant Formation has a negligible source rock potential compared to the Menilite Formation. The Menilite Formation in the Bystřice nad Olší section has mostly "good" source rock potential, although the TOC indicates "very good" potential. The Subchert Member (average TOC: 3.6 wt. %; HI up to 505 mg HC/g TOC) and the Chert Member (average TOC: 2.2 wt. %; HI up to 790 mg HC/g TOC) are the most prolific units. Based on organic petrography and HI, the kerogen is classified as type II and I. Indications of admixtures of type III kerogen are limited to samples with low TOC contents (<1 wt. %). The Source Potential Index (SPI) of the Menilite Formation in the Subsilesian Unit of the Czech Republic is estimated as ~1.15 t HC/m² which is comparable to SPI calculated for sections in the Silesian and Ždánice units in the Czech Republic and for the Waschberg Zone in Austria. Significantly higher SPI values estimated for the Polish and especially the Ukrainian Carpathians (up to 74.5 t HC/m²) are caused by a wider stratigraphic range, several times greater thickness and higher total organic matter content. [ABSTRACT FROM AUTHOR]

Organic matter-rich rocks occur in the Carpathians, both in the Lower Cretaceous and Oligocene. Whereas, the Oligocene Menilite Formation has been intensely studied, the hydrocarbon potential of Lower Cretaceous rocks is less well understood. In the present paper a 405 m thick succession of the lower part of the Shypot Formation in the Chornohora nappe (Ukraine) is studied using 94 outcrop samples. Maturity parameters for the Lower Cretaceous rocks indicate peak oil maturity (~0.85 % Rr) and organic carbon content averages 2.8 wt. % for all samples. As a result of the enhanced maturity, the hydrogen index (88 mg HC/g TOC) and the remaining petroleum potential (2 tHC/m²) are low. Comparisons with coeval rocks from the same tectonic unit, but with lower maturity suggest that the original petroleum potential was significantly higher (4 tHC/m²). Probably about 2 tHC/m² were generated during deep burial (6 km?), but were lost during uplift and erosion. Macerals analysis reveals a mixed type III-II kerogen, with domination of terrigenous components, which is also supported by HI values of nearby marginal mature samples (~200 mg HC/g TOC). Lower Cretaceous organic matter-rich rocks are found along the entire Carpathian arc. A compilation of published data for age-equivalent rocks across the Carpathian Fold-Thrust Belt shows that HI values are mainly controlled by maturity as well as the moderately high original HI values. Most of these rocks contain predominantly type III-II kerogen, whereas Lower Cretaceous rocks in the Skole-Skyba nappe near the Polish--Ukrainian border contain type (III-) IV kerogen. [ABSTRACT FROM AUTHOR]