Structure and Miocene evolution of the frontal Polish Carpathians: a synthesis

Empty AbsThe Polish Outer Carpathians comprise several thrust sheets composed mostly of Cretaceous through Paleogene deepwater siliciclastic flysch. The most external units in the nappe pile is built of the Miocene sediments of the Carpathian foredeep basin. The lower plate (i.e. the sub-Carpathian basement) consists of the generally flat-lying Mesozoic to Permian sedimentary rocks, underlain by tilted blocks of Carboniferous, Devonian and Early Palaeozoic strata that rest on top of Precambrian basement. Top of the lower plate is very rugged; the youngest event that has shaped it was significant erosion post-dating Late Cretaceous – Palaeogene inversion of the Carpathian foreland. This widespread erosion resulted in incision of deep valleys generally directed towards S - SE. The morphology of the sub-Carpathian basement top and the distribution of the Badenian foredeep evaporites were two important factors that have influenced the evolution of the Carpathian orogenic front. A new structural model of the orogenic front and its basement has been recently constructed using outcrops, numerous wells and high quality 2D/3D seismic data.
   In its western segment (Andrychow – Krakow) the Polish part of the Carpathian wedge is characterised by a flat sole thrust located above mostly undeformed Miocene foredeep sedimentary infill overlying faulted Precambrian to Palaeozoic basement.
   Within the tectonic “Gdow embayment” (i.e. tectonic re-entrant), located in the central part of the study area (vicinity of Krakow), thick-skinned structures rooted in the Meso-Paleozoic basement influenced Miocene evolution of the Carpathian front. Miocene compression led to localised inversion of early normal faults, responsible for the formation of small local basin filled by the lower Badenian siliciclastics. Thick-skinned thrust faulting in the pre-Miocene basement was accompanied by thin-skinned back-thrusting and formation of a triangle zone along the Carpathian front within the most external unit built of the Badenian foredeep sediments.
   The central-eastern part of the Carpathian front in Poland between Bochnia and Pilzno is dominated by thin-skinned wedge tectonics induced by combined effect of diverse erosional morphology of the pre-Miocene basement and the areal extent of the Badenian foredeep evaporites. Wedging along the Carpathian front produced well-developed triangle zones of the Miocene Zglobice unit, frequently cored by highly deformed salt succession, including world-famous Wieliczka Salt Mine near Krakow.
   In its eastern segment, the Carpathian orogenic front is defined by shallow-dipping foreland-verging thrusts overlying undeformed Miocene foredeep deposits. In the vicinity of Rzeszow a system of deep paleovalleys has been described, filled in their axial part by the Badenian evaporites.
   Within the easternmost segment of the study area (vicinity of Przemysl) the final stage of evolution of the orogenic front was strongly influenced by the Miocene normal, reverse and strike-slip faulting within the pre-Miocene basement. This complex faulting was caused by Miocene reactivation of the Teisseyre – Tornquist Zone, i.e. crustal-scale boundary between the East European (Precambrian) Craton and the West European (Palaeozoic) Platform.