The study of clastic sediments infilling sedi- mentary basins related to thrust and fold belts represents a fundamental source of information about the evolution of the orogenic wedges that supplied sediment to the basins. Indeed, the basin-fill records the subsidence history within and around the wedge, and, at the same time, the petrology of the sediments records the rock types exposed within the developing orogen. Therefore, the time–space distribution of synorogenic basins, and the composition of their infill, provide funda- mental insights into the dynamics of orogenic wedges and, most of all, into the composition of material eroded from the wedge, which is generally the most difficult to unravel (e.g. Evans & Mange-Rajetzky 1991; Critelli & Le Pera 1994; Garzanti et al. 1996). In this respect, the study of orogen-related basins of the Northern Apennines has previously concentrated on the foredeep basin, which tells us very little about the composition and evolution of the inner part of the system, as it was mainly fed by the Alpine belt (e.g. Gandolfi et al. 1983; Ricci Lucchi 1986; Di Giulio 1999). In contrast, sediments deposited in piggy-back basins, whose distribution and composition are more directly influenced by the dynamic evolution of that part of the wedge, have received less attention. Only recently has a relatively large amount of data been collected from these piggy- back basins – mostly from the oldest, Middle Priabonian–Early Rupelian basin (e.g. Di Giulio 1990; Cibin 1993; Martelli et al. 1998) and the youngest Middle Miocene basin (Spadafora 1995); a first broad synthesis of these data has been published recently (Cibin et al. 2001). This paper develops that synthesis; it focuses on Upper Rupelian–Lower Burdigalian sediments, with the intention of discussing the meaning of provenance changes in clastic units within piggy- back basins, linking this to the geodynamic evolution of the innermost part of the Northern Apennines convergent system, and showing how the provenance study of sediments trapped in piggy-back basins can contribute to the know- ledge of the dynamics of collisional settings. RUNNING HEAD 269 Oligocene–Early Miocene tectonic evolution of the northern Apennines (northwestern Italy) traced through provenance of piggy-back basin fill successions U. CIBIN 1, A. DI GIULIO 2 & L. MARTELLI 1 1 Ufficio Geologico, Regione Emilia Romagna, Viale Silvani 4/3, Bologna, Italy (e-mail: ucibin@regione.emilia-romagna.it)(e-mail: lmartelli@regione.emilia-romagna.it) 2 Dipartimento di Scienze della Terra, Università di Pavia, Via Ferrata 1, Pavia, Italy (e-mail: digiulio@unipv.it) Abstract: The provenance history of sediments deposited in the piggy-back basins of the Northern Apennines has been drawn determining 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 resulting 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 inner- most 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. From: MCCANN, T. & SAINTOT, A. (eds) Tracing Tectonic Deformation Using the Sedimentary Record. Geological Society, London, Special Publications, 208, 269–287. 0305–8719/03/$15.00 © The Geological Society of London 2003.