engleski

Tufa as a Karst phenomena: environmental and palaeoclimate conditions of tufa formation

Tufa is a product of calcium carbonate precipitation under open-air conditions from ambient temperature waters in areas of carbonate bedrock, i.e. karst areas. The carbonate is precipitated in association with a biofilm which is a by-product of the microbial metabolic activity of diatoms, bacteria and/or cyanobacteria. Tufa formation is favoured where well-developed plants exist in streams and waterfalls and this results in different morphological forms. This process is very sensitive to physico-chemical or biological changes in the water and also to seasonal fluctuation, e.g. temperature change. Physico-chemical conditions of tufa precipitation will be presented and compared with conditions of speleothem formation. Geochemistry of tufa formation involves also the isotopic exchange processes of carbon and oxygen isotopes between dissolved inorganic carbon and atmospheric CO2 and by the decisive role of biota. Assuming isotopic equilibrium during calcite precipitation then terrestrial carbonates such as tufa, speleothem or lacustrine sediment can provide a record of environmental and climatic information. Results of investigation of tufa deposits from the Dinaric Karst in terms of the conditions of formation, using physical and chemical parameters in conjunction with isotopic measurements (14C, δ13C and δ18O) will be presented. Variations of growth frequency of tufa deposits based on 14C and 230Th/234U dating demonstrate that the formation of calcite deposits was stimulated by changing climate, e.g. during interglacial periods with warm and humid conditions.

ufa; Dinaric karst; isotopes; calcite precipitation; palaeoclimate

nije evidentirano