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Radiocarbon in freshwater carbonates as tool of Late Quaternary studies

Pazdur Anna

Geologos

2000

Vol. 5

135--154

Different methods of radiometric dating (14C, U/Th, TL) and stable isotopes composition (13C and 18O) in freshwater carbonates are used for analysis of sedimentologic process and reconstruction of paleoclimatic conditions as well as for stratigraphic purposes. Calcareous tufa and speleothems deposited in karst areas seem to be rightly significant indicators of the past changes because of their direct relation to the environment of deposition. Some important methodical and interpretation problems for Quaternary research in Poland were solved during the last ca. 20 years in Gliwice Radiocarbon Laboratory. Synthetic approach to 14C dating of calcareous tufa from Southern Poland, based on statistical analysis of correlation between lithologic type of tufaceous sediment, carbon isotope composition and apparent age was done. Results of measurements of 8lsO and 8I3C in tufa samples dated with 14C method are used to reconstruct Holocene climatic changes in southern and Eastern Poland. The stable isotope composition was used to estimate the mean annual temperatures in the interval 9500-2000 yr BP. On the basis of statistical analysis of several hundred 14C dates for speleothems from Kraków-Wieluń Upland caves warm and cold climate periods were indicated during the last 50,000 years BP. Distribution of the dates indicate that growth of speleothems between 30 and 20 ka BP may be interpreted as reflecting changes of paleoclimatic conditions. Comparison of measured 14C activities in carbonate fractions of lake marl from Gościąż Lake with their varve ages allowed for accurate determination of secular changes of 14C dilution factor of total dissolved inorganic carbon. Basing on the geochemical model developed by Broecker and Walton it was possible to reconstruct mean lake level during the Late Glacial and Holocene. Basing on 14C dates of lithological boundaries in the cores from Gościąż lake basin the changes of lake level during the last 12 ka BP were reconstructed. Paleokarst forms known as “pipes” from Southwest England and South Wales were dated by 14C, U/Th and TL methods. 14C ages were obtained from carbonate cements within sandrock and on the pipe walls. Statistical analysis of dates and geochemical considerations indicate on periods of pipes pipes and pipes infillings.