Compared to coeval successions from the Carpathians, the continuous Jurassic-Cretaceous (J/K) pelagic limestone succession of the Brodno section offers the best possibility to document the J/K passage in a wide area. This section comprises a complete calpionellid, and nannofossil stratigraphic record, that supports the older paleomagnetic data. Moreover, the sequence stratigraphy and stable isotope (δ 18 O, δ 13 C) data gave important results, too, enabling comparison with known key sections from the Mediterranean Tethys area.Key words: J/K boundary, Western Carpathians, regional stratotype, stable isotopes, biostratigraphy, microfossils, pelagic carbonates.
Geological context of the Brodno section: an overviewThe Brodno section is situated in an abandoned quarry on the eastern side of the narrow straits of the Kysuca River Valley north of the town of Žilina (known as the "Kysuca Gate", Fig. 1). It yields a record of hemipelagic marine sedimentation in a marginal zone (the Pieniny Klippen Belt) of the Outer Western Carpathians. The lithology, fossil record (including ammonites and aptychi) and stratigraphy were studied by Andrusov (1938Andrusov ( , 1950Andrusov ( , 1959, Scheibner (1961, 1962, 1967), Borza (1969, Scheibnerová (1969), andSamuel et al. (1988). A more detailed description of the Upper Jurassic and Lower Cretaceous litho-and biostratigraphy was provided by Michalík et al. (1990), Vašíček et al. (1992). Houša et al. (1996) introduced the magnetostratigraphy of the Jurassic/Cretaceous (J/K) boundary beds correlated with the microbiostratigraphic data.This paper discusses the results of an integrated biostratigraphic study using three microplankton groups (calpionellids, calcareous dinoflagellates and nannofossils), as well as stable isotope data (δ 18 O, δ 13 C) in the Brodno section, which is proposed here as the candidate for a West Carpathian regional J/K boundary stratotype. The distribution of the stratigraphically important planktonic organisms revealed several coeval calpionellid and nannofossil bioevents recorded in the pelagic carbonate sequence of the Jurassic/Cretaceous boundary age. The stable isotope data underline environmental changes during the interval studied.According to the International Commission on Jurassic Stratigraphy, it is necessary to search for complete sections, which can provide continuous records of both sedimentation and biotic events across stage boundaries. Although the Brodno section lacks ammonite record, it is presented here as a potential candidate considering its continuously well exposed and biostratigraphically properly documented succession, at least for the West Carpathian region.
Material and methodsThe Jurassic/Cretaceous boundary succession was studied using an integrated sequence-, bio-and isotope stratigraphy approach from the detailed rock section sampled. A quantitative microfacies analysis was carried in thin sections for the sequence stratigraphic pattern of these pelagic limestones (see Reháková 2000a; Michalík 2007). The calpionellids an...