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 beltforedeep 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-thrustmigration 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-thrustflat 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 counterpart 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 shoalwater 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 thefootwall of an active thrust, open toward the foredeep basin.
The Plio-Pleistocene thrust belt-foredeep system in the Southern Apennines and Sicily (Italy)
PATACCA, ETTA;SCANDONE, PAOLO
2004-01-01
Abstract
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 beltforedeep 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-thrustmigration 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-thrustflat 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 counterpart 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 shoalwater 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 thefootwall of an active thrust, open toward the foredeep basin.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
