Geogenic CO2 flux calculations from the Late Pleistocene Tivoli travertines (Acque Albule Basin, Tivoli, Central Italy)

The Lapis Tiburtinus travertine of the Acque Albule Basin(Tivoli, Central Italy) is a well-known travertine deposit composedof ten units separated by unconformity surfaces. This travertinedeposition is related to CO2 degassing of thermal waters circulatingin deep carbonate-sulphate reservoirs. Since for each mole ofcalcite precipitated by groundwater, one mole of CO2 is degassing tothe atmosphere, the volumes of travertine deposits can be used asan indirect proxy of the amount of CO2 degassed during travertinedeposition.In the present work the volumes of the different travertine unitsand the cumulative amount of CO2 degassed per depositional unit(FCO2, which range between 1.56×108 mol a-1 to 5.93×108 mol a-1)have been computed. Furthermore, the fluxes of carbon dioxide perunit area (phiCO2) were computed and compared to the delta18O curve andpollen data.The computed CO2 fluxes, range between 7.11×105 mol a-1 km-2and 2.70×106 mol a-1 km-2. These values are minimum estimationsof the deep CO2 degassing processes because of dissolution anderosion processes and possible CO2 loss from thermal water beforetheir emergence at springs as well as because only the exposedtravertine succession was used as proxy for the entire succession. Thecomparison of the CO2 flux data with the delta18O curve and pollen datashows that smaller variations in carbon dioxide flux are related tochanges in climatic conditions, while greater variations are probablycaused by the increase of the deep CO2 degassing process of the AcqueAlbule hydrothermal system, which is, in turn, relate to the activity ofColli Albani volcanic system.