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Source rock potential of the Miocene sedimentary rocks in the Carpathian Foredeep of the Czech Republic

Geršlová Eva, Medvecká Lujza, Jirman Petr, Nehyba Slavomír, Opletal Vladimir

Geological Quarterly

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2022

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Vol. 66, No. 1

art. no. 1

EN

We determine the organic matter content, its thermal maturity, genetic type, and source rock potential of the Miocene sedimentary rocks in the Czech Carpathian Foredeep. In the Czech Republic the Carpathian Foredeep represents a peripheral foreland basin formed due to the tectonic emplacement and loading of the Alpine-Carpathian Thrust Wedge onto the passive margin of the Bohemian Massif. Random vitrinite/huminite reflectance measurements and maceral analyses were performed on 25 samples from the Carpathian Foredeep succession. Additionally, results of 135 TOC content measurements, 141 Rock-Eval pyrolysis analyses and 27 vitrinite reflectance measurements were used to evaluate the regional distribution and depth trends for the entire Carpathian Foredeep. The thermal maturity of organic matter is between the immature part and peak of the oil window (Tmax = 413–448°C). Beneath the Western Carpathian Thrust Belt, the thermal maturity reaches higher values (Rr = 0.43–0.58%, Tmax = 429–448°C). The hydrocarbon generation potential is poor or fair, even if the total organic carbon values indicate good or even very good source rock potential. This is mainly due to the prevailing gas-prone Type III kerogen. The best source rocks were observed in the Miocene strata of the southern and central segments of the area discussed.

2

Geochemical characteristics, thermal maturity and source rock potential of the Oligocene Šitbořice Member of the Menilite Formation in the Ždánice Unit (Czech Republic)

Jirman P., Geršlová E., Pupp M., Bubík M.

Geological Quarterly

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2018

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Vol. 62, No. 4

858--872

EN

Rocks deposited in the Oligocene Paratethys are recognized as one of the most important source rocks in the Flysch Carpathians. The Šitbořice Member (uppermost NP23 to lowermost NP25 zone) represents the upper part of the Menilite Formation in the Outer Flysch Carpathians of the Czech Republic. This paper presents results of bulk geochemical analysis, Rock-Eval pyrolysis and organic petrography. The geochemical evaluation, source rock potential, kerogen type and thermal maturity were studied using borehole cores. Based on the classification of Peters (1986), the evaluated Šitbořice Member is mostly classified as a “very good” source rock according to TOC and variable, mostly “poor” to “good” according to the petroleum potential. However, the average petroleum potential value assigned the member to “good” source rock which is in accordance with the TOC classification if the “live” TOC is used. A comparable distribution between kerogen type II and III has been indicated by HI. Unlike this, the organic petrography observations show the organic matter belongs to the kerogen type II which corresponds to the relationship of residual hydrocarbon potential versus TOC and HI calculated based on “live” organic carbon. Presumed immaturity was confirmed by Rr and Rock-Eval Tmax. Oxygen-restricted conditions ora dysoxic environment have been indicated by the TOC/TS ratio.

3

Genetic correlation of source rocks and natural gas in the Polish Outer Carpathians and Paleozoic–Mesozoic basement east of Kraków (southern Poland)

Kotarba M. J., Więcław D., Bilkiewicz E., Dziadzio P., Kowalski A.

Geological Quarterly

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2017

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Vol. 61, No. 4

795--824

EN

Natural gas-source rock correlations in the Polish Outer Carpathians and Paleozoic–Mesozoic basement in the Kraków–Brzesko–Nowy Sącz area (southern Poland) have been established. In the Dukla and Sub-Silesian units, mixed kerogen Type-II/III or III/II occurs. The organic matter is immature or low-mature. The Oligocene Menilite beds of the Silesian Unit are rich in TOC and contain gas-prone Type III kerogen of low maturity. In the Paleozoic–Mesozoic basement, the TOC content and residual hydrocarbon potential vary in the Middle and Upper Devonian strata, Mississippian carbonate and clastic facies and Middle Jurassic strata. The Paleozoic strata are capable of thermogenic hydrocarbon generation, while organic matter in the Middle Jurassic rocks is generally immature. Gaseous hydrocarbons accumulated both in the Silesian and Dukla units of the Polish Outer Carpathians and in the Mesozoic basement are genetically related to thermogenic and microbial processes. The Outer Carpathian natural gas was generated mainly from the Type-II/III kerogen of the Oligocene Menilite beds. The thermogenic gases from the Mesozoic basement were generated from Devonian and Mississippian (carbonate) Type-II and mixed II/III kerogens and probably from Silurian/Ordovician Type-II kerogen and Middle Jurassic Type-III/II kerogen occurring at more than 7 km depth. Microbial methane migrated into the Outer Carpathian flysch succession from the Miocene strata of the Carpathian Foredeep.