ISOTOPE AND POLLEN STRATIGRAPHY OF THE TRAVERTINE DEPOSITS AT SERRE DI RAPOLANO, ITALY

Continental carbonates, specifically speleothems, tufas and travertines, are potential archives for peleoclimatic information. Previous studies on speleothems and tufas have shown that these chemical sedimentary rocks provide information about the temperature and isotopic composition of the water from which calcite precipitates. This study aims to assess the potential of travertines, the thermal-water analogue of tufa, as paleoclimatic proxies. A vertical 13m long continuous travertine section from Serre di Rapolano (Siena, Italy) has been sampled and analyzed in high detail for carbon and oxygen isotopes, and for preserved pollens. A total of 750 samples were analyzed for stable isotopes, providing an isotopic profile of the entire section. Ten samples were analyzed for U-Th series age determination and 12 thin sections were prepared for petrographic analysis. U-Th analysis suggests an age range for the travertine from 30-60 ka. Values of δ¹⁸O are from -8.96 to -2.16 per mil, having an average of -5.59 per mil. Values of δ¹³C are from +1.94 to +7.26 per mil, having an average of +4.35 per mil. The isotopic compositions of C and O are well correlated and fit a theoretical model where water temperature variations are the main factor controlling both C and O fractionation. At least 2 sets of isotopic variations are present, with different frequencies. A total of 43 samples were prepared for the determination of pollens. Only eight samples contained enough grains to allow a statistically meaningful count. The most common tree species are Pinus and Cedrus; most of the pollen grains, however, derive from woody and non-woody plants, with a definite predominance of hydrophilic woody plants in the lower part of the section. We attempt an interpretation of the isotopic and palynological data from a paleoclimatic point of view.