Palynological investigation of a Late Quaternary calcareous tufa and travertine deposit: The case study of Bagnoli in the Valdelsa Basin (Tuscany, central Italy)

A Late Quaternary continental succession in central Italy (Bagnoli, Valdelsa Basin) which includes terrigenous and carbonate (calcareous tufa and travertine) sediments was investigated with palynology, 14C dating and stable isotopic techniques. Pollen analyses of 43 samples, including quantification by the Climate Amplitude Method, allowed the documentation of the main palaeoenvironmental, vegetational and climatic changes. Taphonomic biases related to the depositional settings are expressed by i) the significant occurrence of Pinus related to the increase of riverine input/waterborne pollen components in the basal terrigenous strata and by ii) the generally significant presence of herbs, testimony to the local pollen input and dominance of the airborne pollen component in calcareous tufa and travertine. 14C dating on organic samples confirms the Late Quaternary age of the section and the pollen record supports evidence for the onset of carbonate deposition during the Late Glacial Interstadial (LGI), coincident with expansion of thermophilous tree taxa, especially deciduous oaks. Successive cool and dry climate events are attested by the contemporaneous decrease of broad leaved deciduous forest taxa and a rise in herbs. Major unconformities as well as erosional, non-depositional or dissolution events, which interrupt the carbonate deposition at different times in the sequence, are interpreted as a direct response to global climate change and associated to cooler events (i.e. GS-2, GS-1, colder episodes during the LGI). As a whole delta13C and delta18O records do not show any clear relationship to the pollen-derived climatic data or to the carbonate units; rather they reflect a mixing of superficial CO2 and a deeper source, underlining the complex origin of the Bagnoli carbonates.