THE LIMIT OF VARISCAN DEFORMATION IN SOUTHEASTERN POLAND AND THE ORIGIN OF THE LUBLIN SYNCLINE

The extent and character of Variscan thrust sheets in west-central Poland is well known. The limit of these thrust sheets, however, does not mark the limit of Variscan deformation, which is obscured in central and eastern Poland by overlying Mesozoic and Tertiary rocks of the Polish Trough. We present seismic and well data to support the contention that Variscan deformation, as manifest by thin-skinned folding and thrusting, and inverted structures affecting Carboniferous and older strata below the Base-Permian unconformity, extends into the foreland far beyond the mapped limits of the Variscan thrust sheets.

Beyond the limits of the Variscan thrust sheets, pre-Permian strata are intensely deformed into a series of easterly verging fold-thrust structures. The structural level of the region, known as the Radom-Krasnik elevation, is significantly higher than that of the foreland to the east. Devonian and older rocks subcrop the base Permian unconformity with Carboniferous rocks preserved only in the cores of tight synclines. The foreland boundary of the Radom-Krasnik elevation is marked by a large monocline - the Warka-Kazimierz Zone – that is situated broadly above the Teysseyre-Tornquist zone, a long lived and deep seated crustal discontinuity that marks the boundary between the western and eastern European platforms.

The structural level drops significantly across the monocline and folded Carboniferous and Devonian strata are preserved in a broad trough – the Lublin syncline. The Lublin syncline is bound to the north by a cross-fault beyond which pre-Permian strata above the eastern European platform are essentially undeformed. The eastern ‘frontal’ limit of the Lublin syncline is the Koch zone, a triangle zone of classic character. The Kock zone is defined by opposing flaps of Carboniferous and upper Devonian rocks, which are deeply eroded by the Base-Permian unconformity. The vergence of the zone changes along trend from locally relatively symmetrical to more foreland vergent. The Kock zone is cored by intensely imbricated lower Devonian and Silurian rocks. The floor thrust is clearly visible on seismic data though its precise stratigraphic level within the Silurian-Cambrian section is not known because of a lack of critical well data.