Pokuttia deep fault and its influence on tectonics and the oil- and gas-bearing of the south-eastern segment of the Carpathians

https://doi.org/10.23939/jgd2018.02.049
Received: September 12, 2018
Authors:
1
Institute of Geology and Geochemistry of Combustible Minerals of NAS of Ukraine

Objective. The objective of this study is to analyze the influence of the Pokuttia deep fault on tectonics and the oil- and gas-bearing of the south-eastern part of the Ukrainian Carpathians.  Methodology. It is contained in the detailed complex analysis of the geological-geophysical data on the given area. Results. The influence in the Pokuttia deep fault on the flysch structure has revealed itself in the Boryslav-Pokuttia nappe as a series of dislocations with a break of continuity of the north-eastern orientation at the boundary between the Hutsulkyi and Boikivskyi segments with the structures horizontally displaced 10 km off and up to 1,5 km vertically- left-strike slip fault. In the Skyba nappe this is truncation of its front part of the Hutsulskyi segment. In the Dukla-Chornohora nappe and the Bitlya-Svydovets sub-nappe these are sigmoid curvature of their parts in the fault zone with amplitudes of horizontal displacements of up to 10 km. As a result, the Krasnoshora and Hoverla units are joined into single sub-nappe, and the thrust-folds of the Bitlya-Svydovets sub-nappe to a considerable extent are overlapped by it and by the Skupiv sub-nappe. Owing to post-overthrusting vertical movements the Hutsulskyi segment was uplifted during Pliocene-Pleistocene. The rise of the area with the Duklya –Chornohora nappe was the most intensive. The structures of the Bitlya-Svydovets sub-nappe are fragmentally outcropped from under it. In the territory of Romania structurally correspond to them from the north - the thrust-sheet with olistostrome Slon in the Lower Verkhovyna deposits of Oligocene, and from the south - tectonic units Toroklezh and Makla. The Pokuttia fault displaces the Precarpathian regional minimum (amplitude of about 10 km), and the Uzhok deep fault with the signs of right-shift. This is a perceptible impact of the Pokuttia fault on the sub meridional Radekhiv-Viktoriv fault. Sites of intersections of the mentioned faults, so-called knots, if the traps are available, are known to be favourable zones for hydrocarbon accumulation on commercial scales. In the light of new data  on the geological structure of the region the perspective estimate is raised for the structures distinguished of Vorohta-Yasynia (Lazeshchynska, Yasynska and Voronenkivska), as well as Semakivska and Hryniavska, where commercial influxes of hydrocarbons were obtained. This observation also concerns the structures of the basement of the Lopushna subzone of the outer zone of the Carpathean Foredeep under the overthrust of the Carpathians. Scientific novelty. For the first time, using new geological data it was possible to prove the influence of the Pokuttia fault in the zone of its action in a form of the left-strike-slip on the structures of the flysch cover. The structural parallelization of the Bitlya-Svydovets sub-nappe of the Krosno nappe of the Ukrainian Carpathians was carried out with the tectonic units of the Romanian Eastern Carpathians. Interaction of the given fault with the Precarpathian regional minimum and the Uzhok deep fault has a character of the right shift. Areas connected with these dislocations are prospective for hydrocarbon accumulations of commercial value. Practical Value. As a result of investigations essential corrections have been inserted concerning the geological structure of the south-eastern part of the Ukrainian Carpathians. Together with geochemical indications this presents new possibilities in searching for hydrocarbon deposits here.

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