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

Alessandro Mancini (1), Enrico Capezzuoli (2), Andrea Brogi (3,4), Rudy Swennen (5), Lisa Ricci (6) & Francesco Frondini (6)
(1) Department of Earth Science, University of Milan, “A. Desio”, Via Mangiagalli 34, 20133 Milan, Italy. (2) Department of Earth Sciences, University of Florence, Via La Pira 4, 50121, Florence, Italy. (3) Department of Earth and Geo-environmental Sciences, University of Bari, "Aldo Moro", Via Orabona, 4, 70125 Bari, Italy. (4) CNR-IGG - Institute of Geosciences and Earth Resources, Via Moruzzi 1, Pisa, Italy. (5) Geology, Department of Earth and Environmental Sciences, KU Leuven, Celestijnenlaan 200E, 3001 Heverlee, Belgium. (6) Department of Physics and Geology, University of Perugia, Via Pascoli snc Perugia, 06123, Italy . Corresponding author e-mail: alessandro.mancini@unimi.it

The Lapis Tiburtinus travertine of the Acque Albule Basin (Tivoli, Central Italy) is a well-known travertine deposit composed by 10 units separated by unconformity surfaces. This travertine deposition is related to CO₂ degassing of thermal waters circulating in deep carbonate-sulphate reservoirs. Since for each mole of calcite precipitated by groundwater, one mole of CO is degassing to the atmosphere, the volumes of travertine deposits 2 can be used as an indirect proxy of the amount of CO₂ degassed during travertine deposition. In the present work the volumes of the different travertine units and 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 per unit area (φCO₂) were computed and compared to the δ¹⁸O curve and pollen data. The computed CO₂ fluxes, range between 7.11×10⁵ mol a^-1 km^-2 and 2.70×10⁶ mol a^-1 km^-2. These values are minimum estimations of the deep CO₂ degassing processes because of dissolution and erosion processes and possible CO₂ loss from thermal water before their emergence at springs as well as because only the exposed travertine succession was used as proxy for the entire succession. The comparison of the CO₂ flux data with the δ¹⁸O curve and pollen data shows that smaller variations in carbon dioxide flux are related to changes in climatic conditions, while greater variations are probably caused by the increase of the deep CO₂ degassing process of the Acque Albule hydrothermal system, which is, in turn, relate to the activity of Colli Albani volcanic system.

Acque Albule Basin, Lapis Tiburtinus, travertines, climate changes, Carbon Dioxide degassing.