Il bacino di Pornello-Frattaguida e l'evoluzione idrografica plio-pleistocenica tra il F. Paglia e il F. Tevere

The Pornello-Frattaguida lacustrine basin and plio-pleistocenic hydrographic net's evolution between Paglia River and Tiber River

Abstract

The geomorphological, morphoneotectonic, and hydrographic characteristics of the area between the rivers Paglia and Tiber allowed us to understand the evolution of that zone since the Pliocene. In the Upper Pliocene, the hilly belt that links the limestone Apennines to the sea was drained by two main rivers (paleo-Nestore and paleo-Fersinone); these rivers, flowing towards the southwest, formed two distinct, but close, deltas in the Pliocene sea. The beginning of the extensional tectonics led to a general tilting of the area towards the east-northeast. The maximum uplift occurred near the coastline, and the sea regressed westward, resulting in the almost complete emergence of the delta of the paleo-Nestore. At the same time, the northern-central sector of the same area subsided, causing an inversion of the flow of the paleo-Nestore and the formation of the Tavernelle-Pietrafitta lacustrine basin. A fault, corresponding to the Migliari creek, interrupted the flow of the paleo-Fersinone; this led to the formation of the Pornello-Franguida lacustrine basin. To the east, two other depressions (S. Fortunato and Ripalvella swamps) formed; these basins have been filled and drained by the present hydrographic network. To the west, the definitive marine regression left a depressed area where the Fabro swamp was formed; to the south, the sea regression was followed by the establishment of the present hydrographic network, which drained the Fabro swamps (T. Chiani).