Freshwater travertines in the central Apennine (Italy): genesis and climatic and neotectonic significance

The aim of this study is to present, through the use of new geomorphologic, sedimentological and geochemical data, a synthesis of the knowledge of the genesis of freshwater travertine deposits in the calcareous ridge of the Central Apennines (Italy). Different areas in the Umbria-Marche and Latio-Abnuzi Ridges have been chosen as very good examples of typical travertine deposition in the central Apennines. All the areas, even if characterized by different extensions, thicknesses and differences in the hydrochemistry of circulating waters, show similar features (depositional environment, climatic conditions, stmctural and neotectonic conditioning) significant in the reconstnrctiou of the dynamics of travertine deposition. The more or less intense deposition of travertine (very different even in the same area, during different phases) is related to the changing of the hydrogeological conditions in time. Valley deepening, consequent to climatic changes (such as glacial-interglacial transition) andlor periods of more intense tectonic uplift, caused the rapid lowering of the piewmetric surface inside carbonate aquifers; this fact together with climatic improvement increased the hydrologic regime of the rivers, favouring travertine deposition. Subsequently, the process decreased in time, in the same way as a box, filled with water and with a hole in the bottom of it ,progressively empties. Such phenomenon, together with the above mentioned climatic changes which aim at a new equilibrium, seem to be the most important causes of the progressive decrease (and sometimes interruption) of travertine depositional processes. In the Acquasanta Terme area also, where the rising up of thermal water along bctures produced the primary condition for travertine formation, deposition occurred in a fluvial environment, along tributary valleys, on the right side of the Tronto river; this is testified by the presence, at the base and inside the deposit, of alluvial gravely material, fluvial facies and typical "fall" structures. Absolute and relative dating confirmed that travertine formation occurred starting at the end of the Middle Pleistocene and mainly during the transition between glacial and interglacial periods. However, the presence of older deposits (formed in the Early or Middle Pleistocene) in the same areas and that are no longer visible, is not to be excluded