--> --> Tectono-sedimentary Evolution of the Lower Paleozoic Basin Developed Above the East European Craton in Poland and Its Bearing on the Unconventional Petroleum System – New Insight From Regional High-effort Seismic Reflection Data

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Tectono-sedimentary Evolution of the Lower Paleozoic Basin Developed Above the East European Craton in Poland and Its Bearing on the Unconventional Petroleum System – New Insight From Regional High-effort Seismic Reflection Data

Abstract

The Lower Paleozoic basin of Poland has recently been the focus of intensive shale gas exploration activity. The basin developed above the SW edge of the East European Craton and past attempts to use seismic data to understand its structure and evolution have been less than successful due to a variety of factors that have limited seismic energy penetration, not least the thickness of the Upper Permian Zechstein evaporites. This paper presents new geological findings based upon a recently acquired regional, high-effort seismic survey. The survey was specifically designed, in terms of both its location and acquisition parameters, to provide improved sub-Zechstein imaging together with regional structure and thickness variations within the Lower Paleozoic shales along regional 2D profiles connecting the Baltic Basin in the north through to the Lublin Basin in the south-east of the country. The study provided information crucial for understanding the complex tectono-sedimentary history of the basin and its associated unconventional petroleum system. Seismic data has proven that Cambrian – L. Ordovician passive margin succession is unconformably covered by the U. Ordovician - Silurian Caledonian foredeep sequence. The use of PSDM seismic data for the quantitative reconstruction of the evolution of the Silurian foredeep basin has provided estimates of approx. 6km as the minimum depth of burial of the source rock during the Caledonian orogeny. Hitherto undocumented Late Triassic normal faulting affecting the entire cratonic edge, including the Lower Paleozoic shale gas reservoir, can be seen. Within the Podlasie sub-basin, indications of sediment supply from the distal basin margin of the Silurian foredeep have been observed. Data from the Lublin sub-basin shows upper crustal structures down to 20km, including crustal blocks of the Radom-Krasnik High thrust over the crystalline basement during the Variscan orogeny in Late Carboniferous, and deeply-rooted strike-slip fault zones. This basin is also characterised by a large amount of intense Early Carboniferous tectonic deformations related to the reactivation of Precambrian fault zones. Shallower, thin-skinned detached structures within the mid-Devonian evaporites and intra-Carboniferous shales have also been identified. We now have a much greater understanding of the tectonic features that played a crucial role in the evolution of the commercially important Lower Paleozoic sequence in Poland.