Down-Core Magnetic and Microfaunal Variations in the Cretaceous-Paleogene Interval of the Žilina Drill Core, Slovakia.

The Žilina-Hradisko (ZA-1) borehole was drilled near Žilina city, northern Slovakia. The area is known for the continuous sedimentation during Cretaceous and Paleogene, and the K-Pg boundary is developed in Maastrichtian to middle Paleocene plankton-rich marlstones in tectonically inclined sequence. The ZA-1 passes through the light gray Maastrichtian marlstones with rich globotruncanid and heterohelicid microfauna, across the dark grey bioturbated marlstones at the K-Pg boundary. Lowermost Paleocene formation is impoverished in microfauna (disaster species like Guembelitria, Globoconusa), passing to foraminifera-rich marlstones of late Danian formations (recovered species like Parasubbotina, Eoglobigerina). Middle Paleocene formation differs in appearance of large-sized morozovellids, globanonalinids and muricate acarininids. The rock magnetic results show that prior to the K-Pg event, magnetic susceptibility and natural remanent magnetization (NRM) were low. The mixture of low and high coercivity minerals was detected. At K-Pg boundary, susceptibilities and NRM rapidly rise. The elevated and fluctuating values continue through lower part of the Danian Stage. This interval is also distinguished by the presence of superparamagnetic particles, as seen from frequency dependence of magnetic susceptibility, and S-ratio close to 1. The distinctly different magnetic signature of this interval could probably illustrate the paleoenvironmental changes. From upper part of Danian to Thanetian, susceptibilities and NRM return to low and stable values similar to the pre-K-Pg.