Interglacial growth of tufa in Croatia

Tufa samples from the Krka River area in Croatia were dated by C-14 and Th- 230/U-234 methods. The study area is situated in the karst region of the so uthern Dinarides. C-14 ages of 40 tufa samples collected at the waterfalls coincide with the early, Holocene interglaciation, up to 6000 C-14 yr B.P. Comparison of conventional C-14 dates of Holocene tufa and those of speleot hems in the Dinaric Karst shows that speleothem formation started several t housand years earlier than tufa growth. Samples of old tufa deposits from t he Krka River (17) and Plitvice Lakes (12) area and speleothem samples from caves in Dinaric Karst (5) yield 34 230Th/234U dates, most of which cluste r around interglacial marine delta(18)O stage 5 (21). Eight of 13 older dat es belong to interglacial stages 7 and 9; only 5 dates fall within stage 6 and 8 glaciations. Th-230/U-234 dates of speleothems and tufa samples from central Europe have indicated that these were formed preferentially during warm and humid interglacial and interstadial periods, and it appears that t his is true of southern Croatia as well. Stable isotope (delta(13)C, delta( 18)O) analyses of 40 tufa samples from the Krka River area were compared wi th stable isotope analyses of tufa from the Plitvice Lakes area. The delta( 13)C values for both locations are similar and range from -10 to -6 parts p er thousand, indicating similar conditions of tufa formation. A systematic difference between the delta(18)O values of tufa in these two areas reflect s the regional distribution of the oxygen composition of precipitation, (C) 2000 University of Washington.