THE FRESHWATER TRAVERTINE DEPOSITIONS IN CENTRAL ITALY: A CONTRIBUTION OF GEOMORPHOLOGICAL EVOLUTION OF APENNINES (ITALY)

Travertines represent an important deposit in the whole central Apennine: in fact, travertine deposits outcrop in few large areas and in several minor sites, mainly distributed along the Apenninic chain and its west and east piedmont area (i.e. Orte-Roma; Rieti and Valle Velina; Assisi; Pale; Cerreto di Spoleto; Popoli and Tocco da Casauria; Rosara; Civitella del Tronto; Roccamontepiano). They are constituted by groups of lithofacies, evidencing different depositional mechanisms; phytohermal facies, sometimes with phytoclastic gravels and sands intercalated, testify locally high and/or low energy environments (sometimes associated with presence of thermal waters). All deposits show the same depositional environment, developed in fluvial system (characterized by phytohermal barrages, with downstream accretionary sets and upstream dammed areas); this fact is testified by the outcrops distribution (symmetric and parallel to river axis), by the presence of typical fluvial facies and by relationship with alluvial deposits. Travertine mainly forms during interglacial periods (such as Middle Pleistocene, Late Pleistocene and Holocene), when climatic improvement strongly enhance vegetation growth with consequent high amount of dissolved CO2 in infiltrating waters; on the contrary, cold arid phases, favored erosion of the aforementioned deposits and of the underlying bedrock. Valley deepening, consequent to climatic conditions (such as glacial-interglacial transition) and/or periods of more intense tectonic uplift, caused rapid lowering of the piezometric surface inside carbonate aquifers; this fact increased the hydrologic regime of the rivers together with climate improvement, favorable conditions to travertines deposition. Almost all deposits are constituted by several plates located at different heights, from about 100 m up to 900 m a.s.l.; concerning the chronology of deposits, from geomorphological setting and radiometric datations, is possible to award, at the different deposits, an age starting from Middle Pleistocene up to Holocene. Differences in height between Holocene and Pleistocene travertine deposits can be used as further geomorphological evidences of widespread Quaternary uplift; then this study aims at a contribution of knowledge of Quaternary evolution of central Italy, using geomorphological, sedimentological, geochemical and, when possible, chronological data.