Abstract

The high Reggio Emilia-Parma Apennines is one of the more classic and interesting areas of the Apenninic chain. The outcropping tectonic units are the following from the bottom: - The Tuscan Nappe. It consists of an Adriatic-type sedimentary sequence starting from the Upper Trias and reaching the Aquitanian. It begins with quartzites and evaporites (Upper Trias), followed upward by marine calcareous and marly formations (Jurassic and Early Cretaceous in age) sedimented in a contest of mechanical and thermal subsidence. The sequence is closed by Upper Cretaceous-Tertiary shales (the Scaglia toscana Fm) and by an Upper Oligocene-Aquitanian arenaceous flysch (the Macigno Fm) which represents a typical foredeep deposit. - The Modino Unit (Modino-Pievepelago Sub-Unit). It is formed by a basal tectonic melange of Ligurian and Sub-Ligurian origin and by a terrigenous piggy-back slope and basin succession, Bartonian-Aquitanian in age. - The Cervarola succession. It consists of Aquitanian-Burdigalian marly and arenaceous sediments (slope marls, basinal turbidites and pebbly sandstones). It sedimented, East of the Apuane Alps, over the Modino Unit during the outwards movement of the latter. In Burdigalian time the Cervarola succession was overthrust by the Ventasso Sub-Unit.- The Ventasso Sub-Unit. It is formed by a sedimentary succession similar to that of the Modino Unit. - The Canetolo Sub-Ligurian Unit. It is formed by an Upper Coniacian-Upper Oligocene succession sedimented over the Adriatic continental margin. in an intermediate position between the Ligurian and the Tuscan Domain. - The External Ligurian Units (Caio and Ophiolitic Units, the latter limited to a small area in the NE corner of the map). The Caio Unit is made up of a shaly-calcareous basal complex (Lower Cretaceous?- Campanian) and by a Helminthoid flysch (Campanian-Maastrichtian). Both the basal complex and the flysch are alimented by continental Adriatic source-areas and by the Ligurian oceanic ophiolitic lithosphere. Large masses of Triassic evaporites and quartzites ("Scaglie del Secchia") are included, North-East of the Tuscan Nappe front, in the basal part of the "allochthonous", mainly in the Ventasso Sub-Unit. They are interpreted as tectonic slices pulled away from mega-extensional structures (in particular the extensional structure of the Cerreto Pass) and pushed outwards by the allochthonous units. The general setting of the Reggio Emilia Apennines is fairly similar to that of adjacent sectors. The evolution of the Ligurian units is the expression of several extensional (Jurassic) and compression-al phases (Cretaceous and Tertiary). The main compressional phase in the Ligurian Domain is the "Ligurian phase" pre-Upper Eocene in age and, in our opinion, characterized by an "Alpine" vergence. Starting from the Upper Eocene-Lower Oligocene the compressive deformation became Est-verging and progressively migrated outwards, as it is well documented by the closure times of the turbiditic sedimentation in the foredeep and piggy-back basins. The Tuscan Nappe has been affected by an anchizonal deformation characterized by a slaty cleavage in the argillitic layers and by a spaced or pressure-solution cleavage in the more resistent ones. The uppermost successions (M. Modino, M. Cervarola, Canetolo and Ligurian successions) are non-metamorphic and generally characterized by a brittle-ductile deformation, without a pervasive cleavage. The Reggio Emilia Apennines acquired the features of a fold and thrust belt during the Oligo-Miocene phases. The general structure derived from these phases can be compared with that of a duplex, whose roof thrust corresponds with the basis of the Canetolo Unit and whose floor thrust can be supposed within the Tuscan-Umbrian evaporites. The horses of the duplex are well represented in the chain by the structures of the Tuscan Nappe and of the "M. Modino-M. Cervarola complex" (fault-propagation folds and related thrusts).

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