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  • Author or Editor: László Korpás x
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Quaternary thermogene and meteogene travertine occurs globally, both in Hungary and abroad. Size and thickness of the individual deposits are highly variable. They can be classified on the basis of water temperature, morphological setting, depositional environment, microfacies and fabric. All travertine is composed of pure low magnesian calcite and its stable isotopic composition (d13C, d18O) may change according to the facies. Sr and Ba are typical and some places enrichment of heavy metals, U, Th, and REE were also reported. Travertine is generally related to karst water springs; therefore, tectonically-controlled karstification, cave and soil formations are very common. It can be rich in fossils and its water depth varies from some centimeters to tens of meters. Chronology and timing of travertine can be solved by applying numerical, calibrated and correlative methods.

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The Csódi-hegy laccolith belongs to the Middle Miocene Börzsöny and Visegrád Andesite Formation, and is built up by fluidal amphibole biotite dacite. This is a small, typical laccolith as shown by its size (Dl = 11000-1200 m, D2 = 900-1000 m, A ~ 150 m), shape, areal extent of 1 km2 and aspect ratio of 0.08 to 0.14. The fluidal structure of the laccolith is the result of alternation of dark and light bands. The thickness of the bands is in cm-dm scale. This structure and the feeding channels are very well exposed here thanks to quarrying activity. The time span-calculation was performed by counting of the individual bands, by volume estimations and by detailed magnetostratigraphic study. For the calculation of magma transport and growing-time the following assumptions were made: 6-8 km depth of the magma chamber, pressure of 8-10 kbars, temperature of 850-900 °C, a rate of ascent 1 mm/20-36 hours, 15 cm as the average width of a single band, a relative depth for emplacement about 450 m and the volume of the emplaced body of 0.05 km3. A total of 3150 bands were counted along the 330 m-long key section of the laccolith, from the center of the main feeding channel toward both flanks of the body. In this way the calculated total emplacement time for the formation of the Csódi-hegy laccolith varies between 1,100 and 1,900 years. The final episodic kink stage may range from 3 to 6 years and the cooling stage have lasted about 100 years. Volume estimations resulted in similar time spans, varying between 1,800 and 3,300 years. The rapid change from transitional to reverse magnetic polarity may cover some hundreds to some thousands of years.

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The intraformational paleosol and calcareous muddy cavity fills interbedded in the travertine of the Vár-hegy (Castle Hill) in Budapest were analyzed for carbon and oxygen isotope compositions and compared with the isotope compositions of the host travertine. Microscopic investigations of these layers indicate mechanical reworking of the travertine and mixing with the allothigenic siliciclastic material. Micromorphological features, e.g. needle-fiber calcite, carbonate hypocoatings around pores, ferruginous precipitations and clay infillings in the paleosol and cavity fills indicate that in situ pedogenic processes were active in both layers. The presence of ferrihydrite in the A horizon of the paleosol also supports pedogenic alteration. The stable carbon and oxygen isotope compositions of bulk carbonate of paleosol and cavity fills (d13C= -0.6 to 2.1‰ and d 18O= -16.7 to -12.9‰) are very close to the compositions of the host travertine (d 13C=1.1 to 2.1‰ and d 18O = -17.7 to -13.7‰,) and differ from the probable isotope composition of pedogenic carbonate (d 13C values around -11‰). These results indicate that the studied paleosol and cavity fills have only minor pedogenic component (authigenic carbonate content up to 20%); thus the paleosol represents a weakly developed soil, mostly composed of travertine clasts and allothigenic siliciclastic material.

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