Stable isotopes, magnetic susceptibility and nannoplankton and CaCO3 content in the Valanginian Bersek Marl Formation

The Valanginian positive carbon isotope excursion and associated environmental changes, known as the Weissert Event, is the first in the series of Cretaceous Earth system perturbations. Here, we develop a multiproxy cyclostratigraphy from a 31.2-m-thick Upper Valanginian to lowermost Hauterivian section of the Bersek Marl Formation in Gerecse Mountains, Hungary, comprising alternating marlstone layers of varying clay and carbonate content. The bulk carbonate d13C signal shows sustained, elevated values (up to 2.7 per mil) up to 19.2 m, followed by a decreasing trend upsection. Together with biostratigraphic data, this suggests that the lower part of the section was deposited during the plateau phase of the Valanginian Weissert Event. Spectral analyses of the multiproxy dataset, including magnetic susceptibility measurements and gamma-ray spectroscopy on the lower part of the section led to the identification of precession, obliquity, long and short eccentricity signals. A mean sedimentation rate of 14 m/Myr was calculated based on astronomical tuning. The cyclicity in the proxy signals reflects dilution cycles by detrital inputs in the basin, which supports the idea that orbitally-forced humid-arid cycles controlled the pelagic alternating sedimentation during the Early Cretaceous throughout the Tethyan area.