Cretaceous to Palaeogene boundary events and palaeoenvironmental responses across pelagic sequences of the Zilina core section, Slovakia: Rock magnetic, biotic, and geochemical characterization

The Z ˇilina-Hradisko borehole in Slovakia intersects a succession from the Cretaceous Hradisko formation to the Paleocene Hric ˇovske & PRIME; Podhradie formation. In this paper, we mainly focus on the Cretaceous-Palaeogene (K-Pg) boundary interval, which is marked by an abrupt change in planktonic biota and magnetic properties. Micro-palaeontological findings suggest a rapid change from a stable, oxygen-rich, oligotrophic environment during the Maastrichtian to an unstable, cooler environment with reduced oxygenation and evidence of biotic stress in the lowermost Danian strata. An abrupt change in the magnetite concentration in the same interval indicates increased detrital input and probably biogenic (soft) magnetite production. Evidence recorded in borehole with enhanced Hg input into the Maastrichtian Ocean suggests that the Deccan eruptions mostly occurred prior to the K-Pg boundary, whereas no volcanic Hg input was detected at the K-Pg boundary itself. Double peaks in multiple magnetic properties mark the Danian hyperthermal Dan-C2 event, which was characterised by a series of environmental changes, including enhanced terrigenous input, oxygen deficit, increased nutrient supply, high benthic productivity, and Parasubbotina acme. Prior to the Latest Danian event, foraminiferal assemblages were significantly affected by dissolution and oxygen depletion, followed by warming, water column stratification, and diversification of calcareous plankton groups. An increase in detrital input and nutrient export drove the productivity of deep-dwelling subbotinids and globanomalinids and were correlated with the mid-Paleocene biotic event (MPBE). The seafloor biota associated with the MPBE implies oxygen deficiency and the preva-lence of benthic infauna. The Selandian-Thanetian strata markedly differ from planktonic foraminifera of older formations, with their rich content of large, diversified, and heavily calcified morozovellid and igorinid fora-minifera, revealing the existence of water column stratification with surface-water productivity and meso-to oligotrophic conditions. The microfauna of ornate morozovellids and benthic biota from the lowermost forma-tion implies the onset of environmental stress and CaCO3 dissolution during the Paleocene-Eocene Thermal Maximum (PETM).

Automated summary

The Z ˇilina-Hradisko borehole in Slovakia reveals significant changes in planktonic biota, magnetic properties, and environmental conditions across the Cretaceous-Palaeogene (K-Pg) boundary interval. Micro-palaeontological findings indicate a rapid transition from a stable, oxygen-rich environment to an unstable, cooler environment with reduced oxygenation and biotic stress. The presence of increased detrital input and biogenic magnetite production suggests environmental changes during this period. Additionally, major volcanic eruptions occurred prior to the K-Pg boundary, as indicated by enhanced mercury input into the Maastrichtian Ocean.