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

Observations made in different parts of the world on freshwater travertine deposits show that in most cases their formation started during the Early H olocene and generally came to an end. or underwent a strong decline, in the Post-Atlantic. A similar trend seems to have also characterised the previo us warm stages (Interglacials and Interstadials) of the Quaternary. A satis factory explanation of this decline is not yet available even though differ ent hypotheses have been proposed by several authors: some of them point ou t the influence of climatic changes, while others invoke the effects of hum an impact. However, no specific reference has been made to a possible role of groundwa ter temperature changes, notwithstanding their well-known influence on the calcium carbonate dissolution equilibrium. In particular. differences betwe en lower temperature of ground waters (influenced by deep penetration into the limestone bedrock of Late Pleistocene surface temperatures) and the hig her external temperature at the spring may have played an important role. T he infiltrating waters, enriched in CO2 by percolating through the newly fo rmed soils, acquired higher CaCO3 dissolution capacity because of undergrou nd temperatures being colder by several degrees C. The higher temperatures at the emergence, in conjunction with algal-bacterial activity, map have ca used loss of CO2 and travertine deposition. This process may have continued for a long time because of the low thermal capacity of the limestone bedro ck: where ground mater circulated through fissures and channels within larg e volumes of dry rock, and the progressive increase of atmospheric temperat ure during Lower-Middle Holocene. (C) 1999 Elsevier Science Ltd. All rights reserved.