Unravelling source rocks of episutural and foredeep Late Eocene-Miocene arenites of northern Apennines and southern Alps

The Late Eocene to Late Miocene successions deposited along the northern Apennines and southern Alps are re-examined through integration of arenite petrography with fission-track dating on apatite and zircon. Key heavy minerals and rock fragments, chosen as indicators of Austroalpine, Penninic, Southalpine and Ligurian rock associations, have been combined to match with cooling ages of potential source rocks. Northwest of the Val Secchia area, the Late Eocene to late Rupelian wedge-top basins were fed by western sources (Penninic and Ligurian units), while the foredeep basins were supplied from Austroalpine units, with the addition of Southalpine sources from the Early Miocene. Effusive centres conveyed epiclastic sands and pebbles to the sub-Ligurian foredeep but only fall-out deposits to the wedge-top basins during the Rupelian. Non deposition or recycling from Ligurian units occurred in the basins southwest of the Val Secchia structural divide. From late Chattian to Tortonian times, the sedimentary basins migrating on top of the Apenninic thrust system were fed mainly by Ligurian units, with important contributions by the recycling of older wedge-top successions. The Austroalpine basement was the main source also for the Southalpine foredeeps until the uplift of the Southalpine units, as indicated by a marked increase of limestone/dolostone and rhyolite fragments and Jurassic fission-track detrital ages. This tectonic event occurred during the Burdigalian in the Lombardic sector and the during Tortonian in the Venetian sector. Glaucophane is present in small amounts in the late Serravallian-Tortonian Marnoso-arenacea Fm but not in the coeval Venetian foredeep deposits. It is suggested that this mineral was recycled either from epiligurian successions and/or the Chattian-Serravallian succession from the Venetian/Dinaric area.