The upper Pliocene-lower Pleistocene terrigenous deposits of the Southern Apennines and Sicily have significantly contributed to the understanding of the primary relationships between tectonics and sedimentation in an active thrust belt-foredeep system. An integrated stratigraphic and structural investigation allowed the identification of thrust-related depositional sequences with systems tracts defined by specific stratigraphic signatures recording the complex migration path of the active thrusts in the mountain chain. In the foredeep basin, where thrust-related depositional sequences are better preserved, five basic depositional units have been distinguished: 1. Condensed section, underlying at the scale of the entire basin the major truncation surface at the base of the sequence. The deposition of this unit, indicative of a strongly reduced sediment supply, corresponds to a moment of forward transport of the allochthonous sheets over a long thrust flat (active-thrust-flat systems tract); 2. Syn-ramp wedge, made up of a prograding slope-fan system constituted of a thick body of gravity-driven deposits truncated upsection by the active frontal ramp of the allochthonous sheets (active-frontal-ramp systems tract). 3. Onlap-slope system, represented by retrograding basinal deposits onlapping the edge of the allochthonous sheets and featuring a backstepping passive margin (early stage of the backward-thrust-migration systems tract). 4. Transgressive system, made up of basinal deposits matching the maximum marine flooding of the tectonic wedge (late stage of the backward-thrust-migration systems tract); 5. Prograding shelf-margin system laterally grading into a prograding system of basin-floor turbidites (forward-thrust-migration systems tract). In the foreland areas, these depositional units grade into more or less condensed pelagic deposits, with the exception of unit 5 that may laterally pass towards the foreland into a shallower, flexure-related transgressive system. On top of the allochthonous sheets, both the active-thrust-flat systems tract and the active-frontal-ramp systems tract are represented by shallowing-upward shelfal deposits (nappe sheet drape). In an early stage of the backward-thrust-migration systems tract, a retrograding fandelta/shelf system represents in the mountain chain the counter-part of the onlap-slope system. In a late stage, the retrograding fandelta/shelf system is overlain by a muddier transgressive system recording the progressive flooding of the tectonic wedge. The forward-thrust-migration systems tract is commonly represented by a prograding shoal-water delta/shelf system. Two different depositional settings, depending on the trajectories of the active thrusts in the mountain chain, have been recognized: mobile piggyback basin, developed in the hangingwall of an active thrust and flanked toward the foreland by an active ridge; wide passive shelf developed in the footwall of an active thrust, open toward the foredeep basin.
