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Acta Geologica Hungarica
Authors: Sándor Kele, Lászó Korpás, Attila Demény, Péter Kovács-Pálffy, Bernadett Bajnóczi, and Zsófia Medzihradszky

In the area of the town of Tata (Hungary) there are several Quaternary travertine outcrops, of which the Porhanyó Quarry is the best-exposed one. The travertine of the Porhanyó Quarry can be vertically divided into six units. Algal and other phytoclastic and phytohermal grainstone, boundstone and floatstone are the dominant microfacies. On the walls of the quarry carbonate vents and cones were detected; these forms are indicators of former spring activity at the bottom of a shallow lake. The lake, fed by thermal springs, was formed in a siliciclastic floodplain. The upwelling thermal water brought quartz and other detrital grains from the underlying Pannonian siliciclastic sediments to the surface, concentrating them in the vents. The three main phases of lacustrine evolution were interrupted first by a drying and flooding event, followed by a fluvial-eolian event and finally by eolian sedimentation. The oxygen isotope compositions of the vents differ from the values of vertical sections and slope samples, whereas the carbon isotope compositions show less variation. The different facies migrated during the evolution of the Tata Travertine Complex due to changes in morphology and flow direction. The integrated model of lake evolution suggests an upward cooling climatic trend, beginning with a humid Mediterranean climate in the early phase and closing with a cold, dry continental one in the late phase. The Tata Travertine Complex shows a marked d13C difference from the travertine occurrences of the Buda Mts. that is attributed to local effects. The ascending solutions at Tata may have infiltrated through organic-rich bedrocks and could have carried dissolved C enriched in 12C.

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