Tectonostratigraphy of Lake Trasimeno (Italy) and the geological evolution of the Northern Apennines

Trasimeno, a ~ 10 km diameter, shallow (< 6 m deep) lake located in the Central Apennines (Italy) was investigated using an integrated geological/geophysical approach. Single- and multi-channel seismic reflection profiles were collected to reconstruct the geological history of the lake in connection with regional geo-tectonic evolution. Data from the lake, complemented by geological studies of the lake's surroundings, allowed us to recognize that its history is characterized by a rather continuous subsidence driven by normal faults that developed over pre-existing compressional structures. We found that the extensional tectonic regime affecting the entire sedimentary sequence up to the most recent deposits does not show important changes since the lake's formation (Middle-Late Pleistocene) and is probably responsible for its long-term preservation against sediment infill. Our data suggest that during Neogene-Quaternary times the Trasimeno depression developed as: i) a marine gulf in the continental shelf of the Tyrrhenian Sea (Early Pliocene); ii) a wide fluvial plain (Early Pleistocene); iii) a fresh-water lake filling a subsiding tectonic depression (Middle Pleistocene to present-day). Results of this study indicate that the Lake Trasimeno basin can be regarded as a rather efficient recorder of geological events; this might also be the case of other continental shallow-water basins, because these environments favor the acquisition of high-quality geophysical images of the subsurface, and could reveal high-resolution stratigraphic records not common in other continental environments.