Problematiche relative all\u2019analisi mesostrutturale di conglomerati neogenici provenienti da depositi dell\u2019avanfossa, epiliguri e neoautoctoni (Appennino marchigiano-romagnolo).

A mesostructural analysis has been carried out on pebble-cobble surfaces belonging to various formations (Upper Tortonian-Early Pliocene) cropping out between the Savio, Marecchia and Foglia rivers (northern Apennines). The conglomerates occur at different structural levels: 1) in units belonging to the Umbro-Marche-Romagna Sequence, both underlying and overlying the allochthonous deposits of the Val marecchia thrust sheet, 2) in units belonging to the epi-Ligurian Sequence. The analysis of pitted and striated pebbles and cobbles, mesoscopic faults and fractures show evidences of three episodes of tectonic deformations. The first one, characterized by a NE-SW trending subhorizontal extension, is of Messinian age. This extensional episode could be related to the slowing in the outward migration rate of the Apennine deformational front during the late Tortonian-Messinian. The other episodes of deformations, of early Pliocene-Pleistocene age, are characterized by a main subhorizontal shortening direction trending NE-SW, the older one, and NW-SE, the younger one. The episode characterized by the NE-SW shortening direction is probably related to the main tectonic stress field acting in the Northern Apennines during the Neogene. The NW-SE shortening direction is more difficult to explain. It was detected in other sectors of the chain, where was linked to the tectonic activity of local trasverse structural elements. Indeed in the studied area there are transverse (transfer faults) structures that could be linked to this shortening direction. Another hypothesis is that the NW-SE shortening direction can be related to the sinistral transpressive stress field acting in the Northern Apennines during the Pleistocene