Integrated Stratigraphy of Early Lake Pannon Deposits (Late Miocene, Central Europe): Dating Key Outcrops in a Long-Lived Brackish Lake System

Long-lived lakes are exceptional continental systems in the Earth history because their long-term persistence and often isolation promotes evolutionary diversification, endemism, and complex ecological interactions, making them important natural laboratories for investigating links among environmental change, basin evolution, and biotic history. During the Late Neogene (11.6–3.5 Ma), Lake Pannon occupied most of the intra-Carpathian Pannonian Basin System in Central Europe. It was a large, deep, brackish lake (5–12‰ salinity) that was progressively infilled by sediments derived from the uplifting Alps and Carpathians. As in many long-lived lakes, a diverse endemic fauna and phytoplankton assemblage evolved in Lake Pannon, partly from a few surviving marine lineages and partly from freshwater invaders. The birth and early history of Lake Pannon have remained poorly understood. This integrated stratigraphic study, combining macro- and micropalaeontology, magnetostratigraphy, and authigenic 10Be/9Be isotopic dating, therefore focuses on marginal sub-basins of the Pannonian Basin to refine their chronology and provide a new firm chronostratigraphic framework for evolutionary changes. The studied sub-basins and outcrops record contrasting geological histories. At Našice (NE Croatia) the longest deep-water record (11.6–8.0? Ma) spans about 3 Myr from the Sarmatian–Pannonian (Middle–Late Miocene) boundary and is represented by a high-carbonate, low-clastic succession. The Pécs–Danitzpuszta section (S Hungary) also includes the Sarmatian–Pannonian boundary and shows similar early Pannonian deep-water sedimentation, but its profundal calcareous deposits are overlain by sublittoral silt and, by about 10 Ma, by shallow-water sands, yielding a deep-water record of ca. 1.6 Myr. In the Transylvanian Basin, Romania, early Pannonian marls and limestones are absent. At Oarba de Mureş, the Sarmatian–Pannonian boundary occurs within a turbidite succession, yet the early Pannonian mollusc fauna, although less diverse and less abundant, contains the same species as in the Drava region of S Hungary and NE Croatia. The duration of deep-water conditions in the Transylvanian Basin remains uncertain because the youngest deltaic and shallow-water deposits have been eroded, but it can be estimated at about 2 Myr (11.6–9.5? Ma). The Guşteriţa outcrop provides an important window into the otherwise poorly known Transylvanian profundal mollusc fauna (ca. 11.0–10.5 Ma). In the small Şimleu Basin, outcrops reveal a stratigraphic gap between the Sarmatian and Pannonian. Biostratigraphic data constrain the Lake Pannon sedimentary cycle there to 10.6–9.6 Ma, indicating that deep-water conditions persisted for less than 1 Myr. Despite these differences, cluster analysis shows that the early Pannonian deep-water mollusc biota was remarkably uniform across the studied profundal parts of Lake Pannon. Deep-water lymnaeid valencienniins and their ancestor, Radix croatica, were widespread, and their evolution provides a basis for Lake Pannon-wide biostratigraphic correlations. Integrated stratigraphic approaches are therefore essential for reconstructing the geological and environmental history of long-lived lakes and for providing a firm chronostratigraphic framework for future evolutionary or geological studies, including research of raw material resources (hydrocarbon, water, lignite, etc.). The research received financial support from the National Research, Development and Innovation Office of Hungary (NKFIH K 143787 grant).