2nd IGC - Florence, 2004
Abstract title
TUFAS FROM KRKA RIVER (CROATIA): SUITABLE CLIMATIC RECORDS?
Authors
LOJEN SONJA 1, CUKROV NEVEN 2, MIHELCIC GORAN 2, DOLENEC TADEJ 3, VOKAL BARBARA
3
, PAPESCH WOLFGANG 4
presenter's e-mail: sonja.lojen@ijs.si
1
2
3
4
-
J. Stefan Institute, Ljubljana, Slovenia
R. Boskovic Institute, Zagreb, Croatia
University of Ljubljana, Slovenia
Austrian Research Centre, Seibersdorf, Austria
Keywords
tufa
carbon
oxygen
stable isotope
Abstract
Three types of recent carbonate precipitates from the Krka River, Croatia, were analysed:
bulk tufa from 4 main cascades in a 34 km long section of the river flow through the Krka
National Park, a laminar stromatolite-like incrustation formed in the tunnel diverting water
to the hydroelectric power plant close to the lowest cascade and recent precipitates collected
during winter, spring and summer period on different substrates. Stable isotope
compositions of carbon and oxygen in the carbonates, as well as organic carbon in the
sedimentary organic matter were determined and compared to those of water and dissolved
inorganic carbon. The source of DIC was determined from its stable isotopic composition; it
corresponds to the dissolution of CO2 with delta 13-C between -19.5 and -23o/oo VPDB.
Observed difference between measured and calculated temperature of carbonate
precipitation showed that the higher the water temperature, the larger is the error in the
estimated temperature of precipitation. Similar relationship between actual temperature of
precipitation and the error in calculated temperature of travertine formation was observed in
Quaternary travertine north of Rome (Italy), as described by Minssale et al. (2002). This
implies that the climatic signals may be valid only in tufas or travertines precipitated at
lower and relatively stable temperatures. In contrast to findings described in the literature
by several authors, precipitation on artificial substrates did not occur in or close to the
equilibrium conditions on any of the substrates used (glass, wood, copper, natural moss,
plastic scouring pads). Although precipitated under same environmental conditions and
overall water chemistry, the precipitates had different carbon and oxygen isotopic
composition, as well as different delta 13-C of organic carbon. Obviously, different
organisms colonised the substrates and the riverbed, and different substrates favoured
colonisation by different organisms. It is supposed that the surface characteristics of
substrates play an important role in availability of nucleation sites for carbonate
crystallisation and isotope fractionation caused by precipitation/dissolution of metastable
carbonate phases. The colonising biota, on the other hand, can critically change the
microenvironments where precipitation occurs, affecting primarily the carbonate delta 13-C
values.
Reference: Minissale et al., Earth Planet Sci. Lett. 203, 709-728, 2002.
ACCEPTED as Oral Presentation
in session: "G19.01 - Travertines: archives of archeology, neotectonics, and
paleoclimate"
.