The interplay of lithospheric flexure and thrust accomodation in forming stratigraphic sequences in the southern Apennines foreland basin system, Italy

Abstract

Most of the regional shortening in the type area of the southern Italy orogenic belt, Calabria and southern Apennines, was accomodated by displacement on the Calabrian Terrane (Oligocene to middle Miocene), the Liguride and Sicilide Complex (lower to middle Miocene), the Alburni-Cervati-Pollino-Monti della Maddalena units (inner carbonate platform and slope; middle to upper Miocene), Lagonegro units (upper Miocene), the Monte Alpi unit (lower Pliocene) thrust systems. Inception of each thrust system generated synorogenic sediment associated with frontal thrust-tip anticlines or triangle zones and older thrust sheets that were elevated above major ramps farther toward the hinterland. The Neogene kinematic and sedimentary evolution of the southern Italy is related by shortening of the Apennines and Calabria and stretching of the Tyrrhenian Basin. The southern Italy orogenic belt consists of tectonic assemblages of Paleozoic crystalline rocks (various metamorphic rocks and plutonics), Triassic through upper Miocene platform to deep-marine carbonatic and siliceous rocks, Jurassic to Cretaceous ophiolites and related oceanic sedimentary strata, Paleogene to lower Miocene Subduction Complex assemblage, and lower Miocene through Pleistocene foreland clastic strata. Triassic through Quaternary clastic sediments are accumulated in tectonically diverse sedimentary basins, recording the key geodynamic events affected the Mediterranean region after the Late Paleozoic-Early Mesozoic breakup of Pangea. These sediments are generated following the onset of the sequential rift development and continental separation (Triassic to Early Jurassic), the Tethyan proto-oceanic rifting and open-ocean phases (Early-Middle Jurassic to Early Cretaceous), the Tethyan subduction and onset of Alpine orogenesis (Middle-Late Cretaceous to Paleogene), the Adria (or Apennines) orogenesis (early Miocene to present), and the Tyrrhenian backarc rifting (or Tyrrhenian phase; 15 Ma to present). The oldest (early-middle Triassic) siliciclastic sediments of southern Italy are on the Apulia plate (the buried base of the Apulia platform), the Monte Facito Formation of the Lagonegro Basin, and redbeds of Sardinia (Iberian plate). During Upper Triassic to Middle Jurassic, continental redbeds (rift-valley phase), and shelf-slope-basin sediments (proto-oceanic rift phase) having quartzose composition were accumulated directly on the crustal basement of the Iberia plate margin, in Calabria-Peloritani domain, but siliciclastics are absent on the southern Apulia plate. These sediments record the initial phases of the Tethyan rifting processes. Siliciclastic accumulations in southern Italy assemblages during the main alpine phases (Cretaceous to Paleogene) are scarse or absent. The Cretaceous to early Miocene alpine tectonic phases in southern Italy include remnants of the Alpine orogen (Calabrian Block) and quartzofeldspathic siliciclastic deposits of the Oligocene to early Miocene Paludi, Stilo-Capo d’Orlando and Frazzano formations, and volcanolithic, quartzolithic and quartzofeldspathic sands of the Calabro-Lucanian Flysch Unit. The siliciclastic deposits are directly related to new subduction plane of the Adriatic-Ionian oceanic lithosphere beneath the Iberia plate, generating an oceanic subduction complex (Liguride Complex of southern Italy), and a calcalkaline volcanic arc (Sardinia). From late Paleogene to the present, the siliciclastic sedimentary sequences of southern Italy filled basins that are directly related to this convergent setting, causing consumption of the oceanic lithosphere, and subsequent accretion of the Calabrian allochthonous terranes over the Adria-Africa plate, generating post-Oligocene foreland basin systems. The composition as well as stratigraphic and structural relations of clastic sediments derived from erosion of the Calabrian microplate provide constraints for paleogeographic and tectonic models of southern Italy. Clastic detritus in the following sedimentary assemblages were derived mainly from provenance terranes within the strongly deformed Calabrian Arc allochthon: (A) the Paleogene «Calabro-Lucanian Flysch Unit» accretionary wedge, deposited in a remnant ocean basin that lay east of the Calabrian Arc and west of the Adria margin; (B) Burdigalian to lower Messinian foreland basin successions, widely developed in the southern Apennines, representing progressively shifted foredeep basins and related wedgetop basins; (C) Upper Tortonian to Messinian nonmarine to shallow-marine and deep-marine successions, cropping out on the western and eastern Calabrian Arc, representing synrift clastic wedges related to backarc rifting in the peri-Tyrrhenian area (western sequences), or foreland clastic wedges in the peri-Ionian area (eastern sequences); (D) Pliocene and Quaternary of the northern Calabrian Arc, represented by foredeep and related wedge-top basins on the eastern side (Gulf of Taranto and Corigliano Basin), and a slope basin on the western side, the eastern Tyrrhenian margin (Paola Basin). These receive detritus primarily from deep erosion of northern Calabria. The modern deep-marine basins of offshore northern Calabria have many similarities to the middle to upper Miocene clastic sequences in both foreland and backarc regions of the southern Italy. The type of sedimentary provenance of the southern Italy foreland basin system, providing an example of the changing nature of the orogenic belt through time, may contribute to general understanding and application of other major orogens.