Lower Oligocene thrust-system in the epi-Ligurian succession: evidence from the Enza Valley (northern Apennines, Italy)

Abstract

Within the lower part (Upper Eocene–Oligocene) of the epi-Ligurian succession, outcropping in the Emilian side of the northern Apennines (Enza Valley), duplications by thrust tectonics were recognized through the systematic integration of field geology with calcareous nannofossil biostratigraphy. This thrust system, derived from the overthrusting of two thrust-sheets over a footwall, is unconformably overlain by a Rupelian succession. The thrust structure of the Enza Valley, affected by a subsequent wide overturned syncline together with the unconformable succession, shows a remarkable Lower Oligocene contractional tectonics, previously not recognized in the northern Apennines.The comparison of this thrust system with other outcropping areas of the epi-Ligurian succession makes probable the widespread occurrence of the Lower Oligocene tectonics in the uppermost structural levels of the chain (epi-Ligurian domain).In a regional tectonic framework, the Rupelian thrust tectonics affecting the epi-Ligurian succession can be related to the Lower Oligocene closure of the innermost portion of the Subligurian basin (Aveto-Petrignacola Formation) due to the NE-verging overthrusting of the External Ligurian Units. In this context the unconformable succession of the Enza Valley seems correlable with the basal portion of the Subligurian Bratica Sandstone (Rupelian–Chattian) which unconformably overlies a deformed substratum (Mesoalpine Phase). © Elsevier, Paris