Calcareous nannofossils have proved to be very effective in determining the age of Cretaceous flysch sequences of the Northern Apennines. Here, we focus on the beginning of flysch sedimentation, which replaced previous pelagic deposition during the Late Cretaceous convergence stage. In all the examined sequences an early to late Campanian age has been determined for the bases of the flysch formations, implying an essentially synchronous start of orogenesis-controlled sedimentation within the Ligurian Apenninic (Ligurian) Ocean Basin. Data obtained from the siliciclastic turbidite sequence (Vat Lavagna/Mt. Gottero Sandstones) overlying Jurassic ophiolites and sedimentary cover, indicate continuous sedimentation from earliest Campanian to early Paleocene. Thus, either a forearc or 'dormant trench' tectonic setting seems to be required for this sequence. Regarding the calcareous Helminthoid Flysch, a minor diachrony in the basal ages suggest a general younging from south to north. The onset ages of flysch sedimentation range from early Campanian (Southern Tuscany Flysch), to early-middle Campanian (Mt. Caio/Ottone Flysch), to latest Campanian (S. Remo, Mt. Antola, Mt. Cassio, Mt. Caio/Orocco Flysch). This diachrony could be the consequence of Late Cretaceous-early Tertiary transcurrent tectonics in the Apenninic Basin and/or of multiple source areas (from both the European/Iberian and Adriatic margins). These tectonic implications are in agreement with the kinematic evidence of a transpressional regime along the Iberian/Adriatic plate boundary (Apenninic sector) during the Late Cretaceous.
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