Structure and evolution of the Carpathian thrust front between Tarnów and Pilzno (Pogórska Wola area, southern Poland) – results of integrated analysis of seismic and borehole data

Abstract

Seismic data and core from the shallow cartographic Pilzno P-7 borehole were used to construct a new model of the Carpathian orogenic front between Tarnów and Pilzno, in the Pogórska Wola area (southern Poland). The most external, frontal thrust of the orogenic wedge (the Jaśniny structure) was identified as a syn-depositional fault-propagation fold detached above the Upper Badenian evaporites. Its formation was controlled by the presence of mechanically weak foredeep evaporites and by the morphology of the sub-Miocene Meso-Paleozoic foreland plate (Jaśniny and Pogórska Wola palaeovalleys). The frontal zone of the Carpathian orogenic wedge (the Skole thrust sheet and the deformed foredeep deposits of the Zgłobice thrust sheet) is characterized by significant backthrusting of the foredeep succession towards the south, and by the presence of a triangle zone, with strongly deformed Upper Badenian evaporites of the Wieliczka Formation in its core. The triangle zone was formed during the latest thrusting movements of the Carpathians. An indication of the existence of the triangle zone in the vicinity of Dębica has also been provided by reinterpretation of the archive regional geological cross-section. The youngest foredeep deposits, brought to the surface above the backthrust, have been dated as Sarmatian (NN7 nannoplankton zone), which indicates that the latest thrust movements within the frontal Carpathian orogenic in the vicinity of Tarnów–Dębica took place approx. 11–10 million years ago. Thermochronological studies (AFT and AHe) indicated that the foredeep succession drilled by the Pilzno P-7 borehole has not been buried deeper than 1.5–2 km, which is compatible with reconstruction based on the seismic data.