The travertine deposition of central Italy: The accumulation rate reduction under cooling climate during MIS 3

Endogenous travertines are related to fault deformations and climatic conditions which both exert an important control on their deposition. Their study allows us to show the connections between tectonics and climate. The accumulation rates during the MIS 3 time interval (60-30 ka) of three morphologically different deposits of thermogenic travertines from the western sector of central Italy were compared: two large plateaus, Tivoli and Canino, and a much smaller travertine, named Prima Porta Travertine, unearthed in their vicinity. Their chronology was obtained from literature U-Th data. The accumulation rate of these different travertines seems remarkably comparable showing a maximum during 55–46 ka and a sharp decline after 46 ka, which persisted until the end of MIS 3, indicating that it may have been at least a regional-scale event. The Prima Porta travertine was here sampled for a high resolution chemical and isotope stratigraphy and 87 Sr/ 86 Sr ratios. These data partly strengthened previous results, showing that a sharp, well-defined shift in elemental chemistry is connected to the reduction in the accumulation rate. The C and Sr isotopes showed deep carbon provenance but negligible contribution of deep waters in travertine development. It is argued that the elemental change originates from a decrease in the aquifer recharge rates, following the gradual climate transition to an arid and cold stage. This, in turn, had a clear impact on the hydraulic conductivity of faults and fractures and on the upward migration of deep CO 2 fluids, thus removing the conditions necessary for the carbonate precipitation.