Seismic stratigraphy of the Late Miocene sequence beneath Lake Balaton, Pannonian Basin, Hungary

This study is based on the interpretation of about 190 km of high-resolution, single-channel reflection seismic prolifes acquired on Lake Balaton during the GMS93-02 cruise in June of 1993. The seismic survey investigated the lakes subsurface at a maximum depth of about 200 msec down to the acoustic basement, which is represented by Sarmatian (Serravallian) strata. Seismic interpretation showed that the Balaton Quatemary deposits rest above a subhorizontal unconformity marks a major stratigraphic gap that practically encompasses the whole Pliocene and most of the Pleistocene. The Pannonian sequence in turn uncomformably overlies Sarmatian limestone and marl at a depth of 50 to 200 m. Sarmatian strata are truncated at the top by a mature (polycyclic) erosional surface that marks a stratigraphic gap spanning a few million years (about 12 to 9 Ma) and includes the amalgamation of two 3rd-order (with 106 year periodicities) sequence boundaries. These are the top of the Sarmatian sequence (Sar-1 SB) and the top of the lowermost Pannonian 3rd-order sequence (Pan-1 SB). Incised valleys with erosional terrace and channel fills are also recognized from the seismic record.