One basin for two orogens

In the retroforeland of the Western Alps, some syn-orogenic basins have developed since the middle/late Eocene - early Oligocene. The sedimentary successions of these basins recorded the main stages of the Western Alps (neoAlpine events) and Apennines tectonic evolution by regional-scale unconformities that can be correlated across them. This paper focuses mainly on the so-called Tertiary Piemonte Basin (TPB) successions deposited in the southern part of the Alpine retroforeland realm since the late Eocene up to the Messinian. Although the TPB differentiated in partially independent sub-basins, it recorded well, as a unique syn-orogenic basin for the Alps and Apennines orogens, the entire geodynamic history of the Adria-Europe collision in NW Italy. The TPB went from being an Alpine retroforeland basin to being a thrust-top Apennine basin system, as the Western Mediterranean geodynamics experienced the change in the subduction polarity and the onset of the Ligurian-Balearic oceanic spreading. A revision of the TPB stratigraphy and tectono-sedimentary evolution, based on detailed surface and subsurface data integration, is given and compared with data of the Alpine foreland basin on the external side of the Western Alps, of the northern Alpine retroforeland basin (Gonfolite basin) and the Northern Apennine EpiLigurian succession. The resulting interpretive synthesis is constrained by accurate calibration of outcrop geological features, traced at regional scale on an up-to-date continuous geologic map, with some multipanels seismic sections, which cross the whole TPB succession for a total amount of about three hundred km in length. The detailed data integration process provides constraints for critical discussion on the evolution of the Alps-Apennines interference zone.