Migrating foredeep-thrust belt systems in the northern Apennines and southern Alps

Abstract

A tectonic and sedimentary model of the Neogene post-collisional evolution of the South Alpine-Northern Appennines system is proposed. The building of the system took place by the migration of a foredeep-thrust belt complex accompanied by an extensional wave in the backland area of the Apennines. In this model the sedimentary basins are related to different structural zones: foredeep basins, satellite basins and back arc basins. Both in the foredeep and satellite basins, respectively located in front of and over the thrust belt, the migration of the allochthonous cover is evidenced by the displacement of the clastic sedimentary wedges, mainly consisting of turbiditic sequences. Two stages of evolution can be recognized in the foredeep deposits, especially in the Northern Apennines, where an earlier flysch stage, from the Oligocene to the Tortonian, was characterized by the longitudinal spread of the clastic supply mainly coming from the Alps. In a later stage (molasses stage), developed from the late Mioceee onwards, the main feeder to the foredeep was the adjacent apenninic chain. During the evolution of the thrust belt-foredeep system the shifting of the compressional front, and related subsidence axis of the foredeep, was generally continuous. Discrete peaks of movement are recognized in the upper Oligocene, Burdigalian, Serravallian, Tortonian, Messinian and early-middle Pliocene. Several transverse lines bound adjoining segments of the two chains characterized by different rates of outward migration. These transverse lines might be connected to a principal compressional stress acting NNW-SSE, due to the relative movements between the European and African blocks.