New stratigraphic data on the Triassic basement of the Zsámbék Basin — tectonic inferences

Abstract

Middle Triassic basinal carbonates and volcanites (“Buchenstein Group”) representing the oldest formations encountered in the Mesozoic basement of the Zsámbék Basin has been recently exposed in a quarry at the Strázsa Hill near Zsámbék. This succession is overlain by Ladinian to Lower Carnian platform dolomite (Budaörs Dolomite) and a Carnian basinal sequence (Csákberény Formation) exposed in the core Zsámbék Zs–14. The upper part of the Triassic succession is made up by carbonate platform facies of the Upper Carnian – Norian Fődolomit (Main Dolomite) Formation and the Norian Dachstein Limestone.
The structure of the Mesozoic basement of the Zsámbék Basin is mostly determined by the Vértessomló–Nagy -kovácsi Line of W–E strike. This significant structural zone that is covered by Neogene sediments in the basin is exposed in the quarry of the Strázsa Hill. Along this zone the Norian Fődolomit Formation is in contact with the Middle Triassic volcanites and basinal carbonate succession. The re-evaluation of core Epöl Ep–5 led to the conclusion that the dolomite succession below the lower part of the Dachstein Limestone (Fenyőfő Member) is not the Fődolomite Formation as it was supposed earlier, but the Pelsonian Tagyon Formation and there is a tectonic contact between them. The stratigraphic data and the generally steep dipping of the Triassic formations (40–60°) suggest that the extreme widths of the Middle – Upper Triassic dolomite belt comprising the pre-Cenozoic basement of the Zsámbék Basin is probably the consequence of
tectonic repetitions of the successions.