engleski

14C and 230Th/234U dating of tufa and palaeoclimatic significance

Tufa samples were collected at the Krka River which is situated in the karst region of southern Dinarides in Croatia and flows to the Adriatic sea. Different forms of tufa like crystalline aggregates in form of speleothem, compact tufa in form of sandstone and porous tufa were collected from the barriers in water stream, as well as from the old tufa deposits above the present water level. All tufa samples were dated by the 14C method. Samples with 14C ages exceeding the dating limit were dated by the 230Th/234U method. The 230Th/234U age of tufa with high detrital contamination was corrected by isochrone technique. The accuracy of 230Th/234U results was checked by measurements of several tufa samples in two laboratories, in Zagreb and Hannover. 14C and 230Th/234U ages of Holocene samples of compact crystalline material agree well. The porous tufa, where contamination with recent carbonate and thorium detritus or uranium leaching is possible, showed discrepancy of 14C and 230Th/234U ages. Most of tufa samples from barriers in water streams belong to the Holocene or Stage 1 of oxygen isotope time scale. The old tufa deposits belong to the Stage 5 and Stage 7 interglacials. 14C and 230Th/234U results of several speleothems collected in the caves at the Dinaric karst of Croatia also belong to the Stage 1 and Stage 5 interglacials. The joint evaluation of the 14C and 230Th/234U results from Krka River and the Plitvice Lakes region confirms that formation of tufa in Croatia was also restricted to the warm and humid interglacial and interstadial periods.

tufa; radiocarbon; U-Th dating; Dinaric karst; Krka

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