The age and paleoenvironment of a late Miocene floodplain alongside Lake Pannon: Rodent and mollusk biostratigraphy coupled with authigenic Be-10/Be-9 dating in the northern Danube Basin of Slovakia

摘要

We present new age constraints for the late Miocene Volkovce Formation of Slovakia, alluvial facies that accumulated adjacent to Lake Pannon. Facies analysis and authigenic Be-10/Be-9 dating was undertaken at the Bernolakovo and Triblavina localities while the latter outcrop also yielded additional small mammal and mollusk assemblages as well as remains of flora. The results of seven radiometric dating ages yielded a weighted mean age of 9.65 +/- 0.61 Ma for the Triblavina outcrop and 8.85 +/- 0.32 Ma for the Bernolakovo outcrop. The small mammal assemblage at the Triblavina outcrop is indicative of the lowermost MN11 zone, which in the Western European standard definition suggests an age of <8.9 Ma. The similar to 0.1 Ma inconsistency between absolute dating and biostratigraphic dating at the Triblavina outcrop might be explained either by the variation of initial Be-10/Be-9 ratio in the depositional environment or/and by diachronous development of the mammal faunas across the Europe. The mollusk assemblage at this outcrop indicates the paleoenvironment of freshwater lakes affected by rivers with evidence for a nearby riparian forests; it may be roughly correlated with Papp's lithostratigraphic units G and H defined for the Pannonian stage in the Vienna Basin. Our results provide a detailed insight to the late Miocene stratigraphy and terrestrial environments alongside the Lake Pannon shoreline.