Radioisotopic age and biostratigraphic position of a lower Badenian tuffite from the western Polish Carpathian Foredeep Basin (Cieszyn area)

Abstract

The early Badenian interval in the Central Paratethys realm is characterized by a major marine transgression into the Pannonian and Carpathian Foredeep basins. In the western part of the Polish Carpathian Foredeep, Badenian sedimentation started generally with conglomerates (Dębowiec Formation) passing into a thick succession of claystones and mudstones with rare sandstone interbeds (Skawina Formation). Profiles containing a full sequence of lower Badenian strata are relatively rare, and are mainly known from boreholes. In this paper, we present new results on samples taken from such a borehole (Kaczyce K2/07) located near the town of Cieszyn. We focus on reconstructing the chronology of the lower Badenian marine sediments at the beginning of the transgression in the Carpathian Foredeep (lower Skawina Fm.) using radio-isotopic dating (40Ar/39Ar) of a volcanoclastic layer (tuff and tuffite) and biostratigraphy of calcareous nannoplankton and foraminifera.The weighted mean 40Ar/39Ar age for sanidine separates from the tuff provided an age of 14.27 ± 0.03 Ma. This age is consistent with the NN5 and MNN5a nannofossil zones determined in this study. Our foraminiferal assemblages show that the basal beds of the Skawina Formation up to the tuffites correspond to the Orbulina suturalis–Praeorbulina glomerosa Zone (according to Cicha et al., 1975) and cover the interval of the Lower Lagenidae Zone–lowermost Upper Lagenidae Zone (Grill, 1941). The petrographic data from the tuffite allow correlation of the tuffite from the Kaczyce K2/07 borehole to the level of the Chełmek Tuffite Bed (Alexandrowicz, 1997) providing a regional correlation horizon for future studies.