LATE MIOCENE MOLLUSK BIOSTRATIGRAPHY IN THE EASTERN PART OF THE PANNONIAN BASIN (TISZANTUL, HUNGARY)

Biostratigraphic study of Late Miocene (Pannonian and Pontian) endemic molluscs from east Hungarian part of the Pannonian Basin revealed the relative persistence of the deep water association (Paradacna abichi, Dreissenomya digitifera, ''Pontalmyra'' otiophora, Valenciennius etc. ) during the Late Pannonian and Pontian. Consequently, the earlier int erpretation of these forms as Pontian or Lower Pontian ones, and defin ition of the Early and Late Pontian substages by them, should be revis ed. The occurrences of the sublittoral association can be divided into two stratigraphic units: Congeria czizeki and Lymnocardium aff. winkl eri indicate Late Pannonian, while their descendants, i.e. C. zagrabie nsis and L, majeri, indicate Pontian age. In the littoral facies zone 3 stratigraphic units were identified: a Late Pannonian one, an Early Pontian one (with Lymnocardium decorum), and a Late Pontian one (with Prosodacnomya). Evolution from L. decorum to Prosodacnomya took place between 7.7 and 7.0 million years, according to magnetostratigraphic a nd seismic data. Basinward progradation is demonstrated by the geograp hic distribution of molluscs. The Pannonian-Pontian boundary, just lik e the other isochronous surfaces, has a dip towards the interior of th e basin It runs in the delta plain facies in the northern part of the Tiszantul area, further to the south it intersects the slope facies, a nd reaches the basement at the feet of the southeastern Hungarian pre- Neogene highs. Consequently, in the northern part of Eastern Hungary P annonian, and in the southern part Pontian sediments give the major pa rt of the basin fill.