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| Titel |
Uranium-series ages from the Pal-voelgyi Cave, Budapest, Hungary |
| VerfasserIn |
Gyöngyvér Szanyi, Szabolcs Leél-Őssy, Gergely Surányi |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250057502
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| Zusammenfassung |
| One of the most important information in geological research is the age of formation. A
cave’s life is determined by its water content. While water is present in the passages,
dissolution can proceed. As soon as the water-level drops, the erosion of the cave begins.
Some of the cave minerals precipitate under the water level, while others above it. In rare
occasions, minerals arise close to the karstwater surface, thus they are good indicators of
paleo water levels. These minerals can give the most important information about cave
evolution.
Cave rafts start to precipitate on the surface of hot-water lakes. After a thin
film of calcite forms, the moving or dripping water breaks the thin crust and the
broken rafts sink to the bottom of the lake, where precipitation can continue. As a
result, cave rafts of thickness from a tenth of millimetre to a few centimetres can
develop.
Several thermal karstic caves are known in the Rózsadomb area of Budapest, the capital
of Hungary. In this small, 5-6 square km territory, hot water rises along tectonic lines, while
different ion-content water leaks down from the surface and mixing corrosion occurs. With its
more than 13 km length, the Pál-völgyi Cave is the largest cave in the area, in which cave
rafts are very common.
Karstwater and consequently its precipitations are devoid of thorium but contain uranium
at the time of formation, thus their age can be easily determined from the decay equation.
Uranium series age determinations of cave raft accumulations were carried out to investigate
the water level drop in the Pál-völgyi Cave. Samples from different altitudes were collected
and analysed. The dating method is based on 234U/230Th measurements using ICP-MS
analysis, allowing small sample quantities and an upper limit of age determination at cca.
400–500 ka.
Using the ages, the water subsidence history was reconstructed. The water filled out the
main passage level until 320 ka ago. Since then, the water level has been fast dropping, with
an average rate of 0.1-0.2 mm/y. |
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