Kaja Pietsch

Tectonics of the western part of the Polish Outer Carpathians

The western part of the Polish Outer Carpathians is built up from the thrust, imbricated Upper Jurassic-Neogene flysch deposits. The following Outer Carpathian nappes have been distinguished: Magura Nappe, Fore-Magura group of nappes, Silesian, Subsilesian and Skole nappes. Interpretation of seismic and magnetotelluric survey from the region South of Wadowice, allows observation of relationship between basement and flysch nappes in the Outer Carpathians. It also allows identification of dislocation cutting both flysch nappes and their basement. All the Outer Carpathian nappes are thrust over the southern part of the North European Platform. The platform basement is composed of older Precambrian metamorphic rocks belonging to the Bruno-Vistulicum terrane. Sedimentary cover consists of Paleozoic, Mesozoic and Neogene sequences. The characteristic features of this boundary are horsts and troughs of general direction NW-SE, turning W-E. Faults cutting only the consolidated basement and the Paleozoic cover were formed during the Hercynian Orogeny in the Carboniferous and the Early Permian. Most of the older normal faults were covered by allochtonous flysch nappes forming thus the blind faults. During the last stage of the geodynamic development the Carpathians thrust sheets moved towards their present position. Displacement of the Carpathians northwards is related to development of dextral strike-slip faults of N—S direction. The orientation of this strike-slip fault zones zone more or less coincides with the surface position of the major faults perpendicular to the strike of the Outer Carpathian thrustsheets. The huge fault cuts formations from the Paleozoic basement through the flysch allochton between the boreholes in Sucha Beskidzka area. The displacement of nappes of the Carpathian overthrust and diapiric extrusion of plastic formations of the lower flysch units occurred along this fault.

Structure and Plate Tectonic Evolution of the Northern Outer Carpathians

The paper published in previous year (Golonka et al., 2009) was dealing with tectonics of the western part of the Outer Carpathians in Poland. Now, present authors expanded the area of investigation into the central and eastern part of the northern Outer Carpathians (Figs. 1, 2). The structural style of this area was recently refined by seismic survey data, especially from the areas southwest and southeast of Krakow (Fig. 2). This survey was performed by Geofizyka Krakow Ltd. and tied to geophysical and geological borehole and surface data. The authors also utilized the recently published tectonic work, integrating geological and geophysical data (Dziadzio, 2006; Ku]mierek, 2010). The structural style is explained by complex plate tectonic evolution of the Carpathian Mountains and adjacent areas. The Carpathians define an extensive mountain arc, which stretches at a distance of more than 1 300 km, from Vienna area in Austria, to the Iron Gate on the Danube in Romania (Fig. 1). To the west, the Carpathians are linked with the Eastern Alps whereas to the east, they continue into the Balkan mountain chain. Traditionally, the Carpathians are subdivided into their western and eastern parts. The West Carpathians consist of an older, internal orogenic zone known as the Inner or Central Carpathians and the external, younger one, known as the Outer or Flysch Carpathians (Golonka et al., 2005a; ¥lączka et al., 2006). The interpreted seismic survey was located in generally northernmost part of the Outer Flysch Carpathians.

The application of well logging and seismic modeling to assess the degree of gas saturation in Miocene strata (Carpathian Foredeep, Poland)

The presence of natural gas in the pore space of reservoir rocks results in a significant decrease in P-wave velocity. Even low gas saturation can generate seismic anomalies (DHI) and false image of gas accumulation of economic importance. This article presents an attempt to evaluate gas saturation from 2D seismic section in the Miocene sandstone strata in the south-eastern part of the Carpathian Foredeep. The ESTYMACJA program and the Biot-Gassmann model were used to study the dependence between elastic parameters and saturating fluids (water and gas) recorded in wells. Series of calculations was carried out using a method of fluid substitution for various gas saturation. The applicability of seismic data for evaluating gas saturation of reservoir beds was assessed with the use of 1D modelling (synthetic seismograms) and 2D modelling (theoretical seismic section) calculated for different gas saturation. The proposed methodology can be used to identify low and high gas-saturated zones and contour the reservoir.