engleski

Differences in the 14C age, d13C and d18O of Holocene tufa and speleothem in the dinaric karst

We studied Holocene speleothems and tufa samples collected in numerous caves and rivers in the Dinaric Karst of Croatia, Slovenia, Bosnia and Herzegovina, Serbia and Montenegro. Differences in the formation process of tufa and speleothems are discussed in context of their isotopic composition (14C, 13C and 18O), as well as the chemistry of surface water (rivers, lakes) and drip water (in caves).The physical and chemical parameters monitored in the surface water (tufa precipitation) and drip water (speleothem precipitation) show that more stable conditions accompany speleothem than tufa formation. This is particularly obvious in the water temperature variations (2°C-22°C in surface water and 7°C-12°C in drip water) and in saturation index variation (3-11 in surface water and 1-6 in drip water).The range of 14C ages recorded by Holocene speleothems (~12000 yr) is wider by several thousands years than that of Holocene tufa samples (~6000 yr). d13C values for tufa samples range from ?12‰ to ?6‰ and for speleothem samples from –12‰ to +3‰ indicating that the influence of biogenic carbon is more significant for tufa than for speleothem formation.The differences in d18O values of tufa and speleothem samples from different areas reflect different temperature conditions and differing isotopic composition in the water. The study shows that speleothems from the Dinaric Karst can be used as global palaeoclimatic records, whereas tufa records changes in the local palaeoenvironment.

karst; tufa; speleothem; stable isotope; radiocarbon; palaeoclimate; palaeenvironment

nije evidentirano