Travertine deposits of the middle Liri Valley (central Italy): geomorphological, sedimentological and geochemical study. Palaeoenvironmental and palaeoclimatic implications

Abstract

In the middle Liri Valley, between Sora and Fontana Liri, a large plate of travertines outcrops. It has a length of about 10 km, a mean width of 4 km and a thickness from several tens of metres to more than 120 m. The travertine plate, which occupies a palaeovalley carved in a Meso-Cainozoic substratum, has been affected by extension tectonics showing mainly E-W or ENE-WSW trend. Furthermore, it has been eroded and deeply downcut by the Liri river that formed terraced alluvial deposits and/or erosion terraces on its depositional surface or encased in it at different altitudes. The travertine plate is made up of alternating autochthonous and detrital travertine bodies and contains lithofacies associations of different depositional palaeoenvironments, i.e.: fluvio-lacustrine, lacustrine, palustrine, of more or less steep slope and waterfall. The study of their floral and malacofaunal content suggests that the deposition of the studied travertines took place during temperate climatic phases characterized by variations of humidity. Travertines are characterized by low-magnesium calcium carbonate content, ranging from 65 to 100%. Content of major and some trace components are also discussed. Oxygen and carbon isotopic composition of travertines suggest that their deposition took place from mother waters with uniform isotopic composition at relatively steady temperatures. In the ∂18O and ∂13C curves an evident specular behaviour of the two parameters has been noted within the plate, especially for the middle and upper parts of the plate, above the altitude of 188 m. Such behaviour could be a reflection of primary isotopic composition of mother waters, conditioned by climatic factors, by mainly ambient temperature and humidity variations (modality and/or quantity of precipitations), that, in turn, influenced the biological activity. A climatic signal in the compared oxygen and carbon isotopic composition curves is pointed out. As regards the origin of carbon dioxide involved in the formation of travertines it is not excluded that a part of it could be of endogenic origin, the studied area being tectonically active and affected by extensional movements. A sedimentation model, considering mainly depositional phases alternating with mainly erosional or non-depositional phases, likely linked with humidity variations, is proposed. The studied travertines have been deposited in the middle Pleistocene, in a period of time comprised between 360 ka BP and the last interglacial stage.Central italy