engleski

14C dating of carbonate deposits in the Dinaric Karst

14C dating of carbonate deposits in form of speleothems in caves, tufa in river water or lake sediments is based on the fact that a large part of their carbon is of biogenic and/or atmospheric origin. Three factors affect the accuracy and reliability of the 14C age of carbonate samples: 1) the initial 14C activity (Ao) of the carbonate defined as the 14C activity of carbonate sediments at the moment of precipitation, 2) the degree of contamination with allochthonous calcareous deposits and 3) the effect of carbon isotope exchange during the aging of the deposits. The results of 14C dating, of tufa, speleothem and lake sediment samples collected at the Dinaric Karst area of Croatia and Slovenia will be presented. The ranges of 14C ages recorded by Holocene speleothems (~12 000 yr) is wider by several thousand years than that of Holocene tufa samples (~6000 yr). The  13C values for tufa samples range from − 12‰ to − 6‰ and for speleothem samples from − 12‰ to +3‰ in the Dinaric Karst, indicating that influence of soil carbon and/or vegetation impact is more significant for tufa than for speleothem formation. The  18O for tufa samples range from − 11‰ to − 6‰ and for speleothem from — 8‰ to — 4‰ . The difference here is a consequence of the different stable isotope composition and temperature of waters from which the calcite precipitates. Isotope analyses, including  13C,  18O and 14C age values, of tufa, lake sediments and speleothems in the Dinaric Karst confirm that these deposits record environmental and climatic information. While speleothem is a good indicator of global climate and palaeoclimate changes, tufa is a more sensitive indicator of palaeoenvironmental changes.

14C dating; carbonate deposit; Dinaric Karst

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