Dating a long-lived lake in an intermontane basin: Late Miocene Lake Turiec in the Western Carpathians

Lake Turiec existed from Late Middle Miocene to Pliocene in the heart of the Western Carpathians in the intermontane Turiec Basin. Despite the long-lasting lacustrine deposition, which formed a muddy succession up to 900 m thick, specific history of this basin in Western Carpathians has been a puzzle due to the missing geochronological proxies. Authigenic ¹⁰Be/⁹Be dating method was applied to determine the existence duration and regression of the long-lived Lake Turiec. Altogether 35 samples were collected from 11 different localities of the basin representing different sedimentary environments such as lacustrine, fan delta, alluvial fan and braided river. Four different localities, Late Pleistocene alluvial fans Veľký Čepčín and Malý Čepčín, Holocene river floodplains Košťany and Kalamová were considered for determining the initial ratio. The initial ratio from the Veľký Čepčín alluvial fan was used for all other localities representing lacustrine, fan delta, alluvial fan and braided river to determine ages, because it is the only N₀ in agreement with the independent age proxies indicating that the lacustrine deposits cannot be older than 11.6 Ma. Another explanation of the suitability of the Veľký Čepčín initial ratio is its rapid deposition settings, preventing it from alteration by post-depositional processes and interaction with ground water, in contrary to the remaining intial ratio sites. Weighted mean depositional ages calculated using N₀ from Veľký Čepčín imply that the Lake Turiec existed from ~9.96 Ma for more than ~3.25 Myr and regression of the lake begun nearly ~6.71 Ma.

Determining the precise timing of the lake existence will have important implications for geodynamic phases of the Western Carpathians, since it mirrors rapid increase of accommodation followed by intense increase of sediment supply during regression. The presented application of authigenic ¹⁰Be/⁹Be yielded a first radiometric age of long-lived Lake Turiec as compared to roughly estimated age described in previous studies of the Turiec Basin. This novel method also appeared as a promising dating tool to determine the beginning of regression of the lake in an intermontane settings with complicated tectonic and sedimentary history.

The study was supported by the Slovak Research and Development Agency under contract APVV-20-0120.