A balaton alatti pannóniai rétegeket mintázó TFM–1/13 kutatófúrás komplex vizsgálatának eredményei

Correlation of high-resolution water seismic profiles measured at Lake Balaton and Pannonian strata in outcrops and boreholes around the lake was subject of research in the last 30 years. First attempt of a correlation was presented by Sacchi et al (1998, 1999) who suggested that the silicified carbonate cones (geyserites of Loczy (1913)) exposed in the Tihany peninsula could be associated with characteristic high amplitude mounded features identified on seismic profiles. These mounds are situated at the top of a seismic unconformity interpreted formerly as a sequence boundary (Pan-2).To test this correlation a drilling was performed in the eastern basin of Lake Balaton to collect samples from one of the mounds and the underlying beds. Core samples showed lithological features similar to the Feherpart section of the Tihany Member, i. e. clays and siltstone, but no silicified carbonates have been found. Based on their seismic geometry we have interpreted the mounds as slumps that formed in the prodelta of progradational delta lobes deposited between 8.4-8.7 Ma in the Lymnocardium decorum biochron. Gamma-intensity and susceptibility measurements combined with observed lithological features and seismic data also revealed the bottom of these slumps, which is characterized by mollusc shell fragments and centimetre-scale soft-sedimentary deformations.The drill penetrated the Pan-2 horizon, which turned out to be a sharp boundary between clayey and sandy sediments. Be‑isotope ages and reverse magnetic polarity of the core suggest that the formation of this horizon occurred during the C4Ar (9.1‑9.8 Ma) chron, thus is seemingly much older than 7.9 Ma previously suggested by Horvath et al. (2010).