Oligocene-Early Miocene tectonic evolution of the northern Apennines (northwestern Italy) traced through provenance of piggy-back basin fill successions

Abstract

Abstract The provenance history of sediments deposited in the piggy-back basins of the Northern Apennines has been drawn by means of a petrographic study of nearly 200 sandstone samples collected over 250 km of the belt; it allows the evolution of the eroded part of the belt in Oligocene-Early Miocene times to be determined in detail, with special emphasis on the age of the exhumation and the onset of erosion of the high-pressure/low-temperature Pennine metamorphic units of the Ligurian Alps and Corsica that form the innermost part of the chain. Five petrofacies were distinguished, representing three sources that were active separately (three ‘pure’ petrofacies) or together (two ‘mixed’ petrofacies). The resultion sandstone composition reflects the erosion of different source units, changing through time and space along the belt. The stratigraphic distribution of petrofacies records a change in the main clastic source from Ligurian calcareous units to Penninic units. This change occurred over most of the study area, reflecting the complete exhumation of the Penninic metamorphic units within the innermost part of the belt. It occurred at different times along the chain, migrating from northwest to southeast from Late Rupelian to Aquitanian. This time shift is interpreted to be related to the obliquity of the Northern Apennines convergent system.