The role of tectonic activity, topographic gradient and river flood events in the Testina travertine (Acque Albule Basin, Tivoli, Central Italy)

The Acque Albule Basin in Tivoli (Rome, Central Italy) represents one of the largest exposures of travertine deposits in the world. A detailed study of the Upper Pleistocene Testina travertine, constituting the poorly lithified top part of the Lapis Tiburtinus travertines, is presented. Fieldwork performed in an area of 10 km2 and petrographic analysis allow the recognition of six geobodies with different geometries, degree of diagenetic alteration and architectural elements, composed of seven lithotypes. The Testina travertine appears in general as a poorly lithified travertine, even if it shows a high degree of cementation. It is mainly characterised by blocky, drusy or bladed microsparite and sparite calcite cements, related to thermal and meteoric phreatic to vadose water circulation, affecting in particular those travertine deposits located in the northern part of the study area. The Testina, neglected until now in the several studies performed in the Acque Albule Basin, shows a progradational trend from the north to the south and is characterised by environments, evidencing deposition on a gentle slope, in an alluvial plain and in a shallow lake, with gradual transitions between low-energy environments and high-energy environments. Furthermore, based on correlation between the different geobodies in the overall study area, the Testina travertine depositional system was influenced by tectonic activity in the northern part, by an increasing topographic gradient and water discharge flow in the central part and by flooding events related to the Aniene River in the southern part. This study aims to differentiate such influencing factors facilitating the analysis of other travertine depositional systems and also to aid in the interpretation of subsurface analogues, as in the case of South Atlantic Pre-Salt reservoirs.