Abstract

Geological and structural analyses integrated with stratigraphic and sedimentological data allowed for a reconstruction of the architecture of the Tortonian-Messinian chain-foreland system in the outer zone of the Central Apennines. Facies and thickness variations of the siliciclastic deposits belonging to the Tortonian-Messinian Camerino (Calamita et alii, 1979a e b) and Messinian Laga Basins (Centamore et alii, 1991 cum bibl.) indicate the presence of NW-SE trending synsedimentary normal faults which controlled the architecture of the synorogenic basins. These are characterized by troughs, where the greater thickness (about 1000 meters) of the siliciclastic deposits succession (Tortonian p.p.-Messinian in age) are present, bounded on the inner side by structural highs, in which the deposition of hemipelagic sediments (Schlier Formation sedimented until late Tortonian in the Camerino Basin, or Messinian p.p. in the Laga Basin) and Messinian deposits with reduced thickness occurred. Messinian siliciclastic and or evaporitic deposits sealed the normal fault activity in the Camerino Basin, where the main structure is represented by the NE-dipping Camerino fault, bounding the inner side of the siliciclastic basin depocenter. The Camerino Basin architecture is confined to the western limb of the M. S. Vicino-M. d'Aria anticline, related to the M. Sibillini thrust which developed during Neogene, and is a blind structure that does not involve the Oligocene-Miocene sequence located below the Laga basin siliciclastic deposits and shortened by minor detachment folds and related thrusts. The Laga Basin is connected to NE-dipping normal faults recognized along the forelimb of the M. S. Vicino-M. d'Aria anticline, which was also active during deposition of the post-evaporitic member of Laga Fm. This fold nucleated in correspondence with the synsedimentary structural high between the Camerino and Laga Basins. During the Neogene compression, an inversion of the synsedimentary normal faults, and their rotation in correspondence of the forelimbs, occurred. The architecture of the siliciclastic basins is represented in the restored geological cross-sections, where the reconstructed templates show a sort of domino model, typical of an extensional regime, which progressively involved the Apulian foreland, and controlled the depocenter of the synorogenic troughs in front of the Apenninic chain. The reconstructed flexural geometry of the Apenninic chain-Apulian foreland system is characterized by the presence of bulges localized near the front of the chain. They are displaced by foreland dipping normal faults which localize the Tortonian-Messinian siliciclastic basin troughs, that can be interpreted as back-bulge basins. This geometry is in agreement with the flexural model characterized by the presence of a weakness (Waschbusch & Royden, 1992; de Celles & Giles, 1996), inherited and/or developed by a flexural process, which reduced the elastic thickness of the Apulian foreland. Finally, the correspondence of the Umbro-Marchean ridge with the Tortonian-Messinian flexural bulge of the Apulian foreland in roll-back below the Apenninic chain evidences its thrust system geometry heritage.

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