engleski

C and O stable isotopic signatures of fast growing dripstones on alkaline substrates : reflection of growth mechanism, material sources and environmental conditions?

Different forms of dripstones formed on concrete surfaces were collected in different environmental (open-space vs. karstic cave) and climatic (Mediterranean vs. continental) conditions. Spherulitic and rhombohedronic microstructures in dripstones result from changes in the saturation state of the mother solution from which they are formed. Alternations of dark and light laminas indicate growth in dry and wet periods. Large range of δ13C and δ18O values of dripstones was found in different environments (roughly -35.0 to -5.8 ‰ and -22.5 to -5.0 ‰ VPDB, respectively). A strong positive correlation between δ13C and δ18O values indicates isotopic disequilibrium precipitation of CaCO3. The main source of carbon is atmospheric CO2, however, large isotopic differences in δ13C values could also be ascribed to changes in solution pH and different precipitation rates. Increased δ carbon and oxygen values from the apex down the flanks presumably result from the decreasing saturation state of the solution and precipitation rate.

dripstone. secondary carbonate ; concrete ; stable isotopes ; trace elements

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