Lithological Control on thrust-related deformation in the Sassa-Guardistallo Basin (Northern Apennines hinterland, Italy)

The Sassa-Guardistallo Basin (SGB) is located close to the Tyrrhenian Sea and represents one of the most internal Neogene - Quaternary hinterland basins of the Northern Apennines fold-and-thrust belt. Its sedimentary succession consists of ca. 400-m-thick Late Tortonian-Messinian continental -largely conglomeratic -units overstepping a mainly shaly substratum (Palombini Shales) and overlain by Late Messinian evaporites and marine to continental Pliocene-Pleistocene sediments. This stratigraphic succession can be approximated to a composite rheological multilayer that dictated the style of basin deformation. Detailed geological mapping and structural analysis revealed that basin deposits were affected by compressional deformations that can be found both at map and outcrop scales. Decametric splay thrusts emanating from the substratum-conglomerate interface locally double the continental succession and are bounded by a roof thrust along the Late Messinian evaporite décollement, defining a deformation pattern consistent with a duplex-like structure. The time-space structural evolution of the basin inferred from the fieldwork was addressed and tested by analogue modelling that approximated the rheological stratification of the study area to a layered brittle-ductile system. The model results support the hypothesis that the evolution of the thrust system affecting the SGB started as an early floor imbricate fan thrust system that successively evolved to a duplex structure as the link thrusts propagated into the upper décollement layer that resulted from the deposition of the Late Messinian evaporites.