Biostratigraphic significance of calcareous dinocysts in the Tithonian of the Pieniny Klippen Belt (southern Poland)

Biostratigraphic studies of pelagic Tithonian limestones in the Western Tethys are important for regional palaeoenvironmental reconstructions, particularly for determining the onset of the accumulation of Maiolica-type sediments which dominated Early Cretaceous sedimentation in most deep-marine basins. These Tithonian limestones are rich in diverse planktonic microfossils, which constitute the basis of their biostratigraphic framework. In the lower Tithonian, this role is played by calcareous dinocysts, the subject of the present study conducted in the Polish segment of the Pieniny Klippen Belt in the Western Carpathians. Numerous and taxonomically diverse assemblages of these microfossils have been documented within a succession of argillaceous, variegated limestones overlain by whitish Maiolica-type limestones, exposed in a natural outcrop along Szeligowy Creek near Czarny Dunajec. These assemblages include species with stratigraphic significance, particularly those distinguished by differing first appearance datums (FADs). However, our analyses reveal a pronounced diachroneity of these FADs within Western Tethyan assemblages, as demonstrated through correlation of their datum events with the geomagnetic polarity timescale (GTS 2020). This finding underscores the need for caution when attempting stratigraphic correlations between various regions based solely on dinocyst zonations. For this reason, the four biostratigraphic zones identified in our study were correlated with magnetozones exclusively on the basis of data derived from two successions deposited within the same marine basin, for which magnetostratigraphic analyses were carried out concurrently. Based on these correlations, we infer that the onset of Maiolica-type sedimentation in the Pieniny Basin occurred during the younger part of chron M21n, corresponding to the younger interval of the Semiformiceras fallauxi chron in GTS 2020.