Palaeotectonic significance of gravity displacement structures in the Miocene turbidite series of the M. Pollo Syncline (Umbro-Marchean Apennines, Italy)

Abstract

The Northern Apennines are characterized by more or less severely deformed clastic wedges which originated in elongate foredeeps. These foredeeps were generated successively at the expense of the Adriatic Foreland. A thick turbidite sequence accumulated in the Umbro-Romagnan Foredeep during the Middle to Late Miocene. The variability of this sequence indicates that sedimentation and deformation patterns migrated within individual foredeeps. Marked facies and thickness changes were caused by the successive subsidence of foredeep segments in response to ensialic shearing. Subsequent multi-level gravitational spreading resulted in the development of synformal sub-basins at a later stage of the turbidite cycle within the successive foredeep segments. The gravity displacement structures in the M. Pollo Syncline in the Umbro-Marchean Apennines support such a differentiation. Additional ensialic shearing caused the out-of-sequence evolution of some thin-skinned structures. Ultimately, these were preferentially affected by extension tectonics associated with Tyrrhenian crustal stretching.