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Quantitative studies of the calcareous nannoplankton of Sarmatian deposits : case studies in the Sieniawa–Rudka area (Outer Carpathian Foredeep, Poland)

Lelek D., Oszczypko-Clowes M., Oszczypko N.

Annales Societatis Geologorum Poloniae

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2016

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Vol. 86, No. 1

29--57

EN

The aim of this study was the qualitative and quantitative analysis of the calcareous nannofossil assemblages of the Machów Formation, belonging to the supra-evaporitic complex of the Polish Carpathian Foredeep Basin (PCFB). The work was concentrated in the eastern part of the PCFB, in the Sieniawa–Rudka area (Ryszkowa Wola Horst). Samples were collected from the Rudka-13 and Wylewa-1 boreholes. On the basis of calcareous nannoplankton, these deposits were assigned to the upper part of the NN6 Zone combined with the NN7 Zone, which corresponds to the Sarmatian s.s. of the Central Paratethys (upper Serravallian of the Mediterranean scale). Conclusive determination of the biozone NN7 was problematic, owing to the absence of the rare zonal marker species Discoaster kugleri. The typical association of the undivided NN6–NN7 Zone was of low species diversity and usually dominated by Coccolithus pelagicus, Cyclicargolithus floridanus and Reticulofenestra pseudoumbilica (> 7 µm). On the basis of the relative abundance of species, a significant amount of redeposition was deduced. The reworked nannofossils were mostly Eocene in age. The Oligocene, Early Miocene and Late Cretaceous species occurred much less frequently. The dominance of Eocene forms indicates the Carpathians as the main supply area. The Late Cretaceous taxa may have originated from the Senonian marly deposits of the Miechów Trough in the north. Statistical treatment of the quantitative data was performed using multivariate cluster analysis and Nonmetrical Multidimensional Scaling (nMDS). The composition of the calcareous nannofossil assemblages, together with the high percentage of allochthonous taxa, indicate a shallow, coastal environment with a high supply of nutrients.

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Origin of natural gases in the autochthonous Miocene strata of the Polish Carpathian Foredeep

Kotarba M. J.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 3

409-424

EN

Methane concentrations in natural gases accumulated in the autochthonous Miocene strata of the Polish Carpathian Foredeep (between Kraków and Przemyśl) usually exceeded 90 vol%. Methane and part of the ethane were generated during microbial reduction of carbon dioxide in the marine environment, mainly during the sedimentation of Miocene clays and muds. It is possible that this microbial process has continued even recently. Higher light hydrocarbons (mainly propane, butanes and pentanes) were generated during the diagenesis and the initial stage of the low-temperature thermogenic process. Very small changes in the values of geochemical hydrocarbon indices and stable isotope ratios of methane, ethane and propane with depth are evidence for similar gas generation conditions within the whole Badenian and Lower Sarmatian successions. Only in a few natural gas accumulations within the Upper Badenian and Lower Sarmatian reservoirs are thermogenic gases or thermogenic components present, both generated from mixed, type III/II kerogen. These thermogenic gases, now accumulated mainly in the bottom part of Miocene strata, probably resulted from thermogenic processes in the Palaeozoic– Mesozoic basement and then migrated to the Miocene strata along the fault zones. The presence of low hydrogen concentrations (from 0.00 to 0.26 vol%) within the Miocene strata is related to recent microbial processes. Carbon dioxide and nitrogen, which are common minor constituents, were generated in both microbial and low-temperature thermogenic processes. However, CO2 has also undergone secondary processes, mainly dissolution in water during migration. Hydrogen sulphide, which occurs in natural gases of Lower Badenian strata, was most probably generated during microbial sulphate reduction of the Lower Badenian gypsum and anhydrites.

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Origin of liquid hydrocarbons accumulated in the Miocene strata of the Polish Carpathian Foredeep and its Palaeozoic–Mesozoic basement

Więcław D.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 3

443-458

EN

Petroleum geochemical data of 34 oils and condensates accumulated in the Carpathian Foredeep and its Mesozoic and Palaeozoic basement were used to assess their origin and genetic type. The analysed liquid hydrocarbons are characterized by variable densities and sulphur contents. No relationship between these parameters and the reservoir rock age has been found. Secondary processes of evaporative fractionation and biodegradation are evidenced for some oils. These processes proceeded most intensively on the oil from Góra Ropczycka-1K well. The oils from Opaka-1, Lubaczów-157 and Góra Ropczycka-1K wells were generated from organic matter deposited in the Upper Jurassic carbonates. The oil from the inflow in Załazie-2 well originated from the Cambrian strata, but also contains biomarkers characteristic of Miocene strata. The next family, genetically connected with the Silurian and Ordovician source rocks, consists of oils accumulated in the Lower Carboniferous carbonates in Nosówka deposit and in the Upper Jurassic in the inflow into Łękawica-1 well. The condensates collected from the Miocene (Łękawica-1, Pilzno-37, Tarnów-39 and -45 wells) and Upper Jurassic strata (Łąkta-27 and Tarnów-5 wells) were generated by organic matter dispersed in the Middle Jurassic or Lower Carboniferous clastic facies. The remaining oils, from Grobla-Pławowice, Wierzchosławice, Jastrząbka Stara, Partynia-Podborze, Dąbrowa Tarnowska, Brzezówka and Zagorzyce deposits, and the inflows into Tarnów-47 and Pilzno-12 wells were generated from kerogen enriched in organic sulphur usually dispersed in carbonate rocks. Such a type of sediments occurs in the Devonian and Lower Carboniferous strata. Also, these strata as well as the underlying Silurian rocks have sufficient maturity for generation of the discussed oils. The oleanane in the discussed oils most probably originates from kerogen of the Upper Cretaceous or Miocene strata, through which these oils migrated and eluted this biomarker.

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Habitat and hydrocarbon potential of the Palaeozoic source rocks in the Kraków–Rzeszów area (SE Poland)

Więcław D., Kotarba M. J., Kowalski A., Kosakowski P.

Annales Societatis Geologorum Poloniae

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2011

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Vol. 81, No 3

375-394

EN

The quantity, genetic type and maturity of organic matter dispersed in Ordovician, Silurian, Devonian and Lower Carboniferous strata in the basement of the Carpathian Foredeep between Kraków and Rzeszów were determined based on the results of organic geochemical analyses of 600 rock samples collected from 44 wells. The best source rocks were found in the Silurian strata where the total organic carbon (TOC) content is up to 6.6 wt% and the median value equals ca. 1.5 wt%. The median values of the initial organic carbon contents in individual wells vary from 1.2 to 3.5 wt%. The Ordovician, Lower Devonian and clastic facies of the Lower Carboniferous strata can be considered as an additional source of hydrocarbons with the median TOC values of 0.27, 0.56 and 0.53 wt%, respectively. The Middle and Upper Devonian strata as well as the carbonate facies of the Lower Carboniferous strata have much lower quantities of organic carbon, although in these strata levels with elevated TOC contents were observed. In the Lower Palaeozoic and Lower Devonian strata, the oil-prone, low-sulphur Type II kerogen is present, whereas in the younger divisions presence of the gas-prone Type III kerogen is visible. In the Lower Carboniferous clastics gas-prone kerogen dominates. The Silurian and clastic facies of the Lower Carboniferous strata have been deposited in the normal marine conditions, whereas the Ordovician, Devonian and carbonate facies of the Lower Carboniferous strata usually experienced reducing conditions. The source rocks are mostly at the initial and middle phase of the low-temperature thermogenic processes. Locally, immature (in the Lower Carboniferous carbonates in the vicinity of Łąkta gas-condensate field) or late-mature (in the Middle and Upper Devonian strata in the area of Grobla–Pławowice oil field) source rocks were observed.