Applicability and challenges for the authigenic 10Be/9Be dating as revealed by studies from the Pannonian Basin realm

Bourlès et al. (1989: Geochim. Cosmochim. Acta) suggested that authigenic ¹⁰Be/⁹Be ratio could provide a geochronological tool to date deposition of clay-bearing sediment settled in a water column up to 14 Ma old. It is based on ratio of atmospheric cosmogenic radionuclide ¹⁰Be delivered to depositional environments by precipitation and stable ⁹Be extracted from rock massifs by chemical weathering. Determination of the initial ¹⁰Be/⁹Be ratio is essential for efficient application of the dating and may vary spatially as well as in time due to changes in drainage basins, depositional environments, climate, and other factors. The potential of the authigenic ¹⁰Be/⁹Be dating was evaluated during last years in the Pannonian Basin realm, located in Central Europe. This contribution summarizes successful applications as well as discovered problems and challenges, which motivate the ongoing research.

Two initial ¹⁰Be/⁹Be ratios were established from Holocene alluvial and lacustrine clays in the Danube Basin (Šujan et al., 2016: Glob. Planet. Change). The dating was applied to shallow to deep-water sediments deposited in Lake Pannon within the Danube Basin, and helped to constrain paleogeographic changes in the age range of 11.6–3 Ma. Application of the method to the post-rift alluvial succession with high subsidence rates of 50–400 m/Ma in the range of ~9.5–6.0 Ma yielded data consistent with other geochronological proxies (Šujan et al., 2020: Sed. Geol.; Joniak et al., 2020: Palaeo³). The fast accumulation and tectonic quiescence likely provided stable environmental conditions favorable for the dating method applicability.

Lacustrine and deltaic deposits of Lake Pannon were analyzed from cores of Paks boreholes in the central part of the Pannonian Basin. The resulting authigenic ¹⁰Be/⁹Be ages are generally in agreement with magnetostratigraphic age constraints correlated using seismic stratigraphy (Magyar et al., 2019: Földt. Közl.). Outliers with relative enrichment of ¹⁰Be appear in most distal facies, where low terrestrial ⁹Be input is expected.

A study of turbidite deposits from the Transylvanian Basin allowed to compare the established lacustrine initial ¹⁰Be/⁹Be with a ratio independently calculated from Ar/Ar dated horizon (Botka et al., 2019: Austrian J. Earth. Sci.). Majority of samples provided a good fit with other age proxies, while one sedimentary interval exhibits twofold increase of ¹⁰Be/⁹Be probably indicating variability in the environmental conditions (Baranyi et al., 2021: Rev. Palaeobot. Palyn.).

An order of magnitude higher authigenic ¹⁰Be/⁹Be comparing to the established initial ratios were obtained from supposed early Pleistocene sediments from the locality Sollenau in the Vienna Basin. The visual appearance implies, that secondary pedogenic processes might be responsible for a post-depositional input of ¹⁰Be (Willenbring, von Blanckenburg, 2010: Earth. Sci. Rev.). Another case of high ¹⁰Be/⁹Be preventing age calculation was observed in a Pleistocene alluvial environment with intense loess input.

An ongoing research aims to determine the effects of changes in depositional process, sediment source proximity and provenance on the applicability of the dating method. This research was financially supported by the Slovak Research and Development Agency under contract APVV-16-0121 and by the Hungarian National Research, Development and Innovation Office under contract NKFIH-116618.