Palaeozoic palaeogeography of the East European Craton (Poland) in the framework of global plate tectonics

Based on the interpretation of 2D seismic profiles integrated with surface geological investigations, a mechanism responsible for the formation of a large scale normal fault zone has been proposed. The fault, here referred to as the Rycerka Fault, has a predominantly normal dip-slip component with the detachment surface located at the base of Carpathian units. The fault developed due to the formation of an anticlinal stack within the Dukla Unit overlain by the Magura Units. Stacking of a relatively narrow duplex led to the growth of a dome-like culmination in the lower unit, i.e., the Dukla Unit, and, as a consequence of differential uplift of the unit above and outside the duplex, the upper unit (the Magura Unit) was subjected to stretching. This process invoked normal faulting along the lateral culmination wall and was facilitated by the regional, syn-thrusting arc–parallel extension. Horizontal movement along the fault plane is a result of tear faulting accommodating a varied rate of advancement of Carpathian units. The time of the fault formation is not well constrained; however, based on superposition criterion, the syn -thrusting origin is anticipated.

A regional cross-section based on geophysical, borehole, and structural field data reveals the subsurface structure of the western Polish Outer Carpathians, a relatively understudied segment of the Carpathian thrustand- fold belt. A key feature is an antiformal stack, where the Dukla Unit underlies the central part of the Magura Unit. This structure probably was formed due to a thrust ramp within the Palaeozoic cover of the North European Platform. New apatite fission-track ages, along with a re-evaluation of published thermochronologic age data, indicate two exhumation phases. The first occurred in the Early Miocene (~20 Ma), affecting the Magura and Silesian units. The second, in the Late Miocene (~10 Ma), is confined to the Magura Unit and linked to an antiformal stack formation either through underthrusting of the Magura Unit by the Dukla Unit or large-scale normal faulting that drove arc-parallel extension. Both structures are supported by outcrop and seismic evidence. The present authors propose that the lateral termination of the antiformal stack triggered a normal fault system, forming a hanging-wall drop fault along a lateral culmination wall. The structural data of the present study do not support a Middle–Late Miocene arc-perpendicular extension, previously documented in the eastern Polish Outer Carpathians, as a viable explanation for the Late Miocene exhumation, recorded in the western sector.

An attempt was made to describe the quality of the stacked seismic data semi-quantitatively with respect to the spacing of shot and receiver lines. The methods used included: signal-to-noise ratio calculation, seismic-to-well tie accuracy, wavelet extraction effectiveness and reliability of semi-automated interpretation of seismic attributes. This study was focused on the Ordovician-Silurian interval of the Lublin Basin, Poland, as it was considered as a main target for the exploration of unconventional hydrocarbon deposits. Our results reconfirm the obvious dependency between the density of the acquisition parameters and data quality. However, we also discovered that the seismic data quality is less affected by the shot line spacing than by comparable receiver line spacing. We attributed this issue to the fact of the higher irregularity of the shot points than receiver points, imposed by the terrain accessibility. We have also proven that the regularity of receiver and shot point distributionis crucial for the reliable interpretation of structural seismic attributes, since these were found to be highly sensitive to the acquisition geometry.

Reconstruction of initial thickness and geometry of the Lower Palaeozoic strata in the Podlasie and Baltic basins, East European Craton