Extensional basins developed in the western side of the Northern Apennines (Tuscany) since the late Miocene. The Viareggio Basin represents the northernmost of these basins. It is about 85 km long and up to 40 km wide; the basin is oriented NW-SE and bordered by the Mts Pisani to the NE, by the Meloria-Maestra shoal to the SW, and the Mts Livornesi to the SE. Toward the north it closes offshore of Marina di Carrara. The Viareggio Basin has a well-developed offshore and inshore parts and is centered in the Arno River mouth area. The onshore part of the basin is actually covered by continental Quaternary deposits mainly related to the evolution of the Arno and Serchio rivers. Numerous seismic lines cover the basin and can be tied with deep wells. The integrated analysis of these data as allowed the reconstruction of the basin evolution.
The basin is filled by up to 2500 meters of upper Miocene-Present deposits, mainly composed of alternate sand and clay, resting unconformably on the Oligocene-early Miocene Macigno sandstone, the uppermost part of the Tuscan Unit. The basin fill can be subdivided in five unconformity bounded units: lower Messinian littoral marine deposits (Sequence 2), outer neritic lower Pliocene Sequence 4, outer neritic middle-upper Pliocene Sequence 5, and littoral to brackish Sequence 6a (lower Pleistocene) and Seq 6b(upper Pleistocene-Present).
The Viareggio Basin formed in the early Messinian. It evolved as a half-graben during a narrow rift phase in the early Pliocene. In the Quaternary the basin extended toward the east and a new border fault formed along the Mts Pisani. The southern border of the basin is coincident with the Livorno-Sillaro transverse lineament. This lineament experiences a left-lateral movement and strongly influenced the evolution of the basin since the early Pliocene.
Keywords: Neogene, Viareggio Basin, extensional basins, seismic stratigraphy, North Apennines.