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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 Vienna Basin, a major petroleum province in Central Europe, hosts hydrocarbons in stacked carbonate and siliciclastic reservoirs. The study of 84 oil and 51 gas samples in the Austrian sector yields new insights into the petroleum system. The Upper Jurassic Mikulov and Falkenstein formations are the only significant source rocks, which generated oil between 0.7 and 1.0%Rr, and gas between 1.1 and 1.6%Rr. Microbial gas prevails in the southern part of the basin. Biodegradation affects oil down to a depth of 2000 m. Miocene reservoirs in the hanging wall of major faults and oils in transgressive sands are more prone to biodegradation than footwall flysch reservoirs and oils in turbiditic sands in structuralstratigraphic traps. Anaerobic biodegradation results in the formation of isotopically heavy CO2 and isotopically light (secondary) microbial methane. Hydrocarbons in deep carbonate reservoirs are affected by thermochemical sulphate reduction (TSR). While TSR-affected gas is rich in H2S and CO2, TSR-affected oil is characterized by increased dibenzothiophene/phenantrene (DBT/Ph) ratios. In clastic reservoirs, H2S is removed by pyrite precipitation, whereas DBT/Ph ratios remain high. Hence, high DBT/Ph ratios may be used as proxy for TSR. Stable sulphur isotopes signatures confirm Upper Triassic anhydrites as the main sulphur source for H2S. [ABSTRACT FROM AUTHOR]

The Eggerding Formation, typically about 45 m thick, forms part of the deep marine Oligocene succession in the Molasse Basin, which comprises from bottom to top the Schöneck (formerly "Fish Shale"), Dynow ("Bright Marlstone"), Eggerding ("Banded Marl") and Zupfing formations ("Rupelian Marl"). The Eggerding Formation and the lower part of the Zupfing Formation have been studied using core and cuttings samples and a multidisciplinary approach involving core description, geochemistry, palynology and nannopaleontology. The Dynow Formation and the lower part of the Eggerding Formation were deposited during nannoplankton zone NP23 (Martini, 1971). The transition between the Dynow and Eggerding formations is characterized by a gradual decrease in carbonate contents. The Eggerding Formation deposited in near-shore environments contains several sand layers. In contrast, the Eggerding Formation deposited along the northern slope is generally poor in sand. Its lower part consists of dark grey laminated shaly marlstone with white bands rich in coccolithophorides. TOC contents are about 5 %. The upper part of the Eggerding Formation consists of a homogenous sequence of marly shale and includes in average 1.6 % TOC. Oxygen deficient conditions prevailed during deposition of the Eggerding Formation. Marine palynomorphs are present in all samples from the Eggerding Formation, but calcareous nannoplankton is restricted to its lower part. Salinity variations are recorded in rocks of the lower part of the Eggerding Formation. The environment during deposition of its upper part was more stable. Log signatures, which are comparable over tens of kilometres, provide evidence for the lateral continuity of the Eggerding Formation deposited on the upper slope. Slope instabilities are indicated by slumps and extensive submarine slides. Sliding reached a maximum at the transition from the Eggerding to the Zupfing Formation, when locally a succession up to 70 m thick was removed from the northern slope. The slided material was redeposited either on the northern slope or at the base of the slope. The Eggerding Formation is overlain by the Zupfing Formation (NP24), consisting of clay marl up to 450 m thick. Oxygen-depleted conditions continued during deposition of the Zupfing Formation, but only the lowermost few meters of the Zupfing Formation ("Transition Zone") are rich in organic matter (1.5 % TOC). Whereas the lower part of the Eggerding Formation (TOC 1.9-6.0 %; HI up to 600 mg HC/g TOC) holds a very good source potential for oil (and gas), its upper part and the Transition Zone (TOC: ∼1.5 %; "true" HI 500-600 mg HC/g TOC) are characterized by a good potential. Biomarker data suggest that the latter contributed significantly to the Molasse oils. In contrast, the contribution of the Dynow Formation and the lower Eggerding Formation was minor. [ABSTRACT FROM AUTHOR]