Influence of climatic changes on freshwater travertine deposition: A new hypothesis

Abstract

Observations made in different parts of the world on freshwater travertine deposits show that in most cases their formation started during the Early Holocene and generally came to an end, or underwent a strong decline, in the Post-Atlantic. A similar trend seems to have also characterised the previous warm stages (Interglacials and Interstadials) of the Quaternary. A satisfactory explanation of this decline is not yet available even though different hypotheses have been proposed by several authors: some of them point out the influence of climatic changes, while others invoke the effects of human impact.However, no specific reference has been made to a possible role of groundwater temperature changes, notwithstanding their well-known influence on the calcium carbonate dissolution equilibrium. In particular, differences between lower temperature of ground waters (influenced by deep penetration into the limestone bedrock of Late Pleistocene surface temperatures) and the higher external temperature at the spring may have played an important role. The infiltrating waters, enriched in CO2 by percolating through the newly formed soils, acquired higher CaCO3 dissolution capacity because of underground temperatures being colder by several °C. The higher temperatures at the emergence, in conjunction with algal-bacterial activity, may have caused loss of CO2 and travertine deposition. This process may have continued for a long time because of the low thermal capacity of the limestone bedrock, where ground water circulated through fissures and channels within large volumes of dry rock, and the progressive increase of atmospheric temperature during Lower-Middle Holocene.