Authigenic 10Be/9Be as a tool for epicontinental basin chronostratigraphy: Refining the Late Miocene-Pliocene history of the southern Pannonian Basin and Fruška Gora Mts.

Authigenic ¹⁰Be/⁹Be dating is increasingly used to constrain the depositional ages of marine and continental sedimentary successions that lack suitable material for conventional geochronology. Cosmogenic ¹⁰Be is produced in the atmosphere through cosmic-ray interactions with nitrogen and oxygen and is subsequently delivered to the Earth’s surface by wet and dry deposition, whereas stable ⁹Be is released primarily by continental weathering and transported to depositional basins by rivers. Following their delivery to the basin, both isotopes are scavenged from the water column and incorporated into authigenic Fe–Mn oxyhydroxides and other reactive sedimentary phases. The depositional age is calculated from the radioactive decay of authigenic ¹⁰Be relative to ⁹Be, requiring an independently constrained initial authigenic ¹⁰Be/⁹Be ratio representative of the sediment at the time of deposition. However, variations in sediment provenance, depositional processes, beryllium sources, reworking of older successions, and post-depositional redistribution may modify either the initial ratio or its subsequent preservation, complicating the application of the method in epicontinental basins. The determination of initial ratio is therefore a crucial aspect of the method application. 

The Pannonian Basin has been extensively studied using authigenic ¹⁰Be/⁹Be dating over the past 13 years, with hundreds of samples processed. This research has also focused on determining the initial ratio, with analyses of Holocene river-floodplain sediments providing reasonable estimates. A dataset of 55 samples revealed minor but clear variation in initial ratios between ∼3-6 x 10^-9. In this approach, the palaeoriver responsible for deposition of the dated succession is identified, and the initial ratio of the corresponding present-day stream is applied in the age calculation. Although empirical and unable to account for temporal changes in provenance and denudation rates, this approach yields ages consistent with independent geochronological constraints where available.

This contribution presents newly acquired results from the southern Pannonian Basin and the Fruska Gora Mts. The region experienced a complex evolution during the Late Miocene-Pliocene, as the normal regression of Lake Pannon, recorded by prograding shelf-slope systems from several directions, was complicated by the onset of basin inversion. This caused uplift of the basin margins synchronously with subsidence in the central depocentres. Moreover, another lacustrine water body, termed Lake Slavonia or Lake Paludina, developed after the regression of Lake Pannon and was associated with deposition of the Viviparus Beds. The relationship between Lake Pannon and Lake Slavonia or Paludina remains unresolved.

The first set of dating results comes from borehole cores penetrating the regressive succession above shelf-slope clinoforms in the Szeged Basin, yielding an age of ∼5 Ma. A fluvial succession exposed on the flanks of the Fruska Gora Mts. at Čerević yielded ages of ∼4.5 Ma and probably represents channels that fed Lake Pannon. The succession representing Lake Paludina in the Sremski Karlovci clay pit yielded an age of ∼3.8 Ma. Interestingly, a comparable age was obtained from a fluvial succession exposed farther west at Ilok, which probably represents channels that drained towards Lake Slavonia.

The study was supported by the Slovak Research and Development Agency under the contracts APVV-20-120 and APVV-23-0227.