I travertini della Valle del Pescara tra Popoli e Tor de' Passeri (Abruzzo, Italia Centrale)

Abstract

Travertine deposits occurring in the Pescara Valley between Popoli and Tor de' Passeri-Piano d'Orta in the Abruzzi region (Central Italy) have been examined. Their geomorphologicai attitude has been determined and the following studies have also been carried out on these deposits: facies analysis, mineralogical and petrographical composition, several U-series and 14C datings. The fades analysis allowed the identification of the depositional environment of the travertines composed mainly of phytoclastic lithotypes, containing lens-shaped bodies of mainly inorganic ooids, of palustrine, fluvial and fluvio-lacustrine environment. Tabular phytoclastic deposits have been sedimented in basins closed by natural dams composed mainly of autoctonous lithotypes, organized in fan-shaped step-like terraces, prograding downstream. Two main travertine dams have been observed in the area: the first one, located near the Bussi railway station, caused the formation of the Popoli and Bussi sul Tirino travertine plates; the second, located in the Tor de' Passeri-Piano d'Orta area, caused the formation of a basin that extended upstream as far as the Gole di Popoli. The Tocco da Casauria plate was formed at the same time as the above mentioned deposits on a paleosurface high on the righthand side of the Pescara valley. The plate represents a large deposit composed of palustrine-lacustrine lithotypes in the lower part evolving to a fan-shaped steplike terraced body. The deposition of travertine seems to have taken place since the beginning of the Upper Pleistocene, following an important erosional phase that cut deeply in the substratum to a depth of 504-60 m below the present-day river-bed, and continuing through the Upper Pleistocene up to the Holocene. During this period the travertine deposits have been subjected to erosional phases that have dissected them deeply, causing also the formation of fluvial terraces. In the studied area four orders of local terraces have been mapped; particularly developed are the terraces of the second order in the Decontra and Vicenne areas (Upper Pleistocene) and the third order terrace of Tor de' Passeri-San Clemente area (Holocene-Upper Pleistocene). The terrace of the fourth order of Piano d'Orta (Holocene) is less evident. The mentioned terraces have been dated by means of U-series and 14C methods and are between 33.000 and 4.000 years BP old.