Evidence of associated deposition of travertine and calcareous tufa in the Quaternary carbonates of Valdelsa Basin (Tuscany)

Abstract

E. Capezzuoli et al., Evidence of associated deposition of travertine and calcareous tufa in the Quaternary carbonates of
Valdelsa Basin (Tuscany). (IT ISSN 0394-3356, 2008).
The Quaternary continental deposits discontinuously exposed in the southern part of the Valdelsa Basin, represent four orders of terraces corresponding to four Late Pleistocene-Holocene fluvial/palustrine synthems formed as a consequence of the tectonic uplifting of Southern Tuscany. In most of the Elsa River network the terraces are composed of detrital deposits (mixed, siliciclastic-carbonate silty sands with lenticular interbeds of gravels), but locally, along specific segments of the valleys, the detrital sediments are replaced by lenticular bodies of concretionary limestones made of massive, sometimes highly porous, calcareous tufa that, only in the
upstream areas, are interbedded with laminated facies with tabular geometry and fabric typical of travertine.
The distribution the different facies can be observed in the upstream part of the Imbotroni Valley in the locality of Bagnoli (SE of San
Gimignano - Siena). Their relationships records the development of a complex depositional system controlled by the intermittent outflow of a thermal spring alternated to seasonal/meteoric fresh water input. When the thermal spring was active, the warm waters fed proximal, shallow pools were well laminated travertine facies were deposited while faraway from the spring and/or during the periods of prevailing meteogene, fresh water input, the massive phytoclastic/phytohermal calcareous tufa formed.
A similar depositional evolution appears to have developed at the beginning of all the Quaternary carbonate synthems formed in the
Valdelsa Basin, thus explaining the anomalous distribution of the concretionary carbonate deposits, limited only to a segment of the
Elsa fluvial network.