Use of Quaternary travertines of central-southern Italy as archives of paleoclimate, paleohydrology and neotectonics

Abstract

: A. Bertini et al., Use of Quaternary travertines of central-southern Italy as archives of paleoclimate, paleohydrology and
neotectonics. (IT ISSN 0394-3356, 2008).
This paper reports how travertine of central-southern Italy, formed in response to the extensive circulation of waters inside the regional aquifer hosted in the Mesozoic carbonate sequences, can be used as a tool for paleoclimatic, neotectonic and paleohydrological investigations.
CO2-rich thermal springs, CO2 vents and travertine are frequent occurrences of the peri-Tyrrhenian sector of central-southern Italy. In
a crust affected by mantle magmas triggering fluids motion, among others CO2 from several horizons at variable depth, the δ13C of
CO3-ions of dissolved travertine suggests the type of circulation and the prevalent CO2 source involved. More negative values suggest
“normal” topographically driven circulation in karstic circuits, where CO2 derives from soil (bacteria); more positive values suggest the
inflow into the karstic circuits of deep CO2. Such rising CO2, together with other acidic gases (e.g. H2S) greatly enhances limestone
dissolution. Accordingly, the travertine formed at the surface (metheogene vs thermogene) reflects the type of “mother” CO2 involved
in the dissolution process. In this way, travertine can be used to trace the evolution of paleohydrothermal systems in areas where
there are no thermal features at surface.
In terms of tectonic tool, since active and fossil travertine in the Apennines can be found at very different elevations, their formation
age reflects the difference in elevation between the present and the past karstic circulation. Being the Apennines a young, very active
orogen, the described methodology of using travertine as a benchmark for paleohydrology, suggests for a vertical isostatic rate of 0.7
mm/y.
Being very sensitive to environmental conditions, travertine can also be used as a tracer for paleoclimate. The parallel investigation on
the stable isotopic composition (δ18O, δ13C) of the dissolved CO3-ions, and palynological profiles in two Pleistocene deposits of central Italy (Serre di Rapolano and Tivoli, the latter in progress), allowed to describe variations in the last ca 120 kyrs. The correspondence between observed environmental fluctuations in pollen and isotopes, as well as with other proxies in nearby terrestrial deposits, and with more global proxies (ice-core and foraminifera) seems possible and demonstrates that travertine can be used to investigate the paleoclimate of the late Quaternary. This is in line with the observation that most of dated travertine in central Italy cluster in interglacial periods. This coincidence seems reasonable: 1) because the deposition of travertine is depending upon rainfall amounts, and 2) because in glacial periods, the lower level of the oceans also lowers the base level of karstic circulation.