The Barga Basin (Tuscany): A record of Plio-Pleistocene mountain building of the Northern Apennines, Italy

Abstract

The Barga Basin, located between the Apuane Alps and the Northern Apennines, was the site of a fines-dominated meandering alluvial plain during the Early-Middle Pliocene. Rivers came from the Tyrrhenian side, across the Apuane Alps, and carried gravels mostly composed of Tuscan units that capped the metamorphic complex. Apatite fission tracks indicate that the metamorphic core of the Apuane Alps was deeper than 4 km. To the east, the Apennine divide did not exist and the area was part of the Po plain. A major unconformity marks the transition to the Late Pliocene–Early Pleistocene sequence, mostly made of metamorphic gravels deposited by braided rivers still coming from WNW. At ca. 2 Ma, the Apuane Mountains, following uplift, underwent severe denudation. Wind gaps along the Apuane ridge suggest that the drainage still partially extended westward in the area that is now drowned under the Ligurian-Tyrrhenian sea. Since the Early Pleistocene, rapid uplift of the Apennine Ridge led to the present-day drainage and the deposition of two alluvial terraces. The older terrace at Monte Perpoli is scarcely represented while the Late Pleistocene one is made of large west-flowing telescopic alluvial fans. Since late Early Pleistocene, uplift of the Apennine divide, associated with the activity of high-angle normal faults, generated reversed rivers. During this period the activity of the Versilia fault isolated the Apuane ridge and further drowned the eastern Ligurian basin. A new interpretation and timing of the tectonic evolution of this sector of the Apennine and the adjacent Tyrrhenian sea and peri-Adricatic Basin emerges.