Polyphase thrusting in piggy-back deposits: the example of epi-Ligurian Succession (northern Apennines, Italy)

A Lower Aquitanian thrusting phase has been recognized for the first time within the piggy-back deposits of the northern Apennines (epi-Ligurian Succession) outcropping in the Enza Valley. This result, together with previous structural and biostratigraphical data, indicates the existence of thrusting at the uppermost structural level and allows us to delineate a polyphase tectono-sedimentary evolution of the Middle Eocene-Lower Miocene epi-Ligurian Succession characterized by two successive northeast-thrusting phases (Rupelian and Lower Aquitanian) separated by unconformable deposits developed between Rupelian and Chattian. These thrust tectonics, at lower structural levels, can be related to the northeast-verging overthrusting of the Ligurian Units onto the Subligurian Units. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.