Memoria di Salvatore Critelli

Transcription

1 Rend. Fis. Acc. Lincei s. 9, v. 10: (1999) The interplay of lithospheric flexure and thrust accomodation in forming stratigraphic sequences in the southern Apennines foreland basin system, Italy Memoria di Salvatore Critelli 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 Frazzanò 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 wedge-

2 258 s. critelli top 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. Key words: Mediterranean; Southern Italy; Sedimentary Basins; Tectonics; Clastic Sedimentation. Riassunto. Relazioni tra flessurazione della litosfera e messa in posto delle falde nella formazione di successioni stratigrafiche del sistema di bacino di avampaese dell Appennino meridionale, Italia. Le relazioni stratigrafiche, composizionali e strutturali delle successioni sedimentarie clastiche dell Appennino meridionale permettono di contribuire quantitativamente ai modelli tettonici e paleogeografici del sistema orogenetico dell Italia meridionale. I sedimenti clastici delle successioni sedimentarie post-oligoceniche erano derivati principalmente dalle unità tettonostratigrafiche alloctone dell arco calabro settentrionale. Le relazioni stratigrafico-composizionali dei sedimenti clastici dei bacini sedimentari interposti tra la microplacca calabra e quella adriatica implicano che la flessurazione litosferica della placca adriatica in congiunzione con l accomodamento tettonico delle falde cristalline calabridi sono stati importanti fattori di controllo nello sviluppo della sedimentazione del sistema di bacino di avampaese sudappenninico. Il carico litostatico causato dalla messa in posto delle falde calabridi sopra la placca adriatica, dal Miocene inferiore all attuale, hanno causato la deformazione flessurale della litosfera adriatica, producendo aree depresse profonde (bacino di avanfossa), aree lievemente innalzate (forebulge) e aree lievemente depresse (bacino di back-bulge). La migrazione verso est della flessurazione litosferica avveniva ad impulsi in risposta del trasporto verso est della catena a falde calabra. Nel tempo le aree occupate dal forebulge, a seguito degli spostamenti della catena a thrust verso est, venivano incorporate nel bacino di avanfossa. The Problem. Introduction This paper focuses on clastic sedimentation developed during the sequential history of an orogenic system, in the Mediterranean Region. These clastic trends, covering a large time span from Early Mesozoic to the present, may contribute: (1) to the paleogeographic and paleotectonic reconstructions of the southern Italy portions of the western Mediterranean orogen, and (2) to the general models of complex relationships between clastic sedimentation and paleotectonic history of other major orogens. The evolutionary record of Earth s processes preserved in the form of sedimentary rocks has been pivotal in paleogeographical and paleotectonic reconstructions of source/basin systems. Compositional trends of clastic strata through space and time are used to infer the structural history of adjacent mountain belts and to monitor the key geodynamic changes during orogenic processes (e.g. Dickinson, 1985, 1988). The controls on the composition and dispersal pathways of clastic strata along the convergent plate margins have long been debated (e.g. Dickinson, 1988; Ingersoll et

3 the interplay of lithospheric flexure and thrust accomodation ::: 259 al., 1995). Clastic infilling of sedimentary basins in orogenic systems have been used as important indicators of tectonic activity and climatic changes. In the orogenic systems, clastic sedimentation may record the accretionary processes, the accomodation of the thrust units, and the flexural features of the foreland plate. The development of an orogenic wedge during continental collision results in thickening of the crust. The excess mass of this thickened crust acts as a load on the underthrust plate, causing it to be flexed downwards close to the load, so developing a foreland basin (e.g. Beaumont, 1981; Sinclair and Allen, 1992). During plate convergence, the vertically acting load of the mountain belt migrates over the foreland plate, thus resulting in the migration of the associated foreland basin. The foreland is the region between the front of a thrust belt and the adjacent craton (e.g. Dickinson, 1974; Bally and Snelson, 1980; Allen et al., 1986; Miall, 1995). Large volumes of clastic sediment are derived from erosion of the thrust belt and deposited in the foreland basin. The foreland basin generally is defined as an elongate trough that forms between a linear contractional orogenic belt and the stable craton, mainly in response to flexural subsidence caused by thrust-sheet loading in the orogen (fig. 1). Foreland basin stratigraphy records tectonic, eustatic, and climatic changes at convergent plate margins (e.g. Miall, 1995). The formation of unconformities is the results of the interplay of temporal variations in the erosion and lateral progradation rates of the orogenic wedge, as well as tectonic and eustatic sea-level changes (e.g. Beaumont, 1981; Jordan, 1981; Schedl and Wiltschko, 1984; Peper et al., 1995). Approach and Scope. This paper presents results of regional structural, stratigraphic and provenance relationships that constraint the post-oligocene tectonic history of the southern Apennines foreland basin system (fig. 2). The paper focuses on the effects of tectonic deformation along the Adria and the Calabrian microplates on siliciclastic sedimentary sequences during sequential history of the growing orogen in southern Italy. The stratigraphy, composition and dispersal pathways of the southern Apennines clastic sediments is interpreted using relationships between stratigraphic record and structural evolution of the fold-thrust belt to contribute to (1) the paleogeographic and paleotectonic reconstruction of the southern Apennines orogen and (2) the general models on sedimentary history of foreland basin systems. The key stratigraphic sequences of the southern Italy orogenic system are here described using new data and interpretations, or re-interpreting previous published data. The entire stratigraphic, compositional and structural data set are interpreted using new general models of sequential evolution of foreland basin systems. The Calabrian microplate is one of the fragments of continental crust of the western Mediterranean that rifted off the southern margin of the Iberian plate and drifted southeastward to collide with the Adria plate (e.g. Smith, 1971; Dewey et al., 1973, 1989; Biju-Duval et al., 1977; Cohen, 1980; Bouillin, 1984; Malinverno and Ryan, 1986; Channel and Mareschal, 1989; Patacca et al., 1990, 1993; Doglioni, 1991; Vai, 1992; Stampfli and Marchant, 1997; Gueguen et al., 1997, 1998; Cello and Mazzoli,

4 260 s. critelli Fig. 1. Diagrammatic cross sections showing the generally accepted notion of foreland-basin geometry (a, b) and the relationships of lithospheric flexure to accomodation space in foreland systems (c to e) (e.g. Giles and Dickinson, 1995; De Celles and Giles, 1996). a) General relationship between fold-thrust-belt, foreland basin and forebulge; b) foreland-basin geometry and depozones: wedge-top, foredeep, forebulge and back-bulge depozones; c to e) relationship of the flexural features in times; c) is the initial (Time 1) foreland system; d ) foreland evolution during accretion of the fold-thrust-belt at Time 2; forebulge is migrated cratonward; e) previous forebulge is assembled within the fold-thrust-belt. Modified after Giles and Dickinson (1995), and DeCelles and Giles (1996). 1999) (fig. 3). Exhumation of the Calabrian crustal terranes during rapid uplift and erosion since middle to late Oligocene to about 10 Ma (Thomson, 1994, 1998) has produced abundant clastic sediments that accumulated in 1) a Late Paleogene remnant ocean basin (the Liguride Complex), 2) numerous Neogene foredeep and wedge-top depozones of the foreland basin system of the growing orogenic belt and flexed Adria passive margin, and 3) since Late Tortonian, foreland basins and backarc syn-rift troughs (Critelli and Le Pera, 1998) (fig. 4). The modern physiography and geology of Calabria are the result of post-30 Ma geodynamic processes in which synchronous accretionary processes were active along the eastern flank (northern Ionian Sea), and rifting processes along the western flank (Eastern

5 the interplay of lithospheric flexure and thrust accomodation ::: 261 Fig. 2. Present day distribution of the main geodynamic domains of the Alpine region. Modified after Stampfli and Marchant (1997).

6 262 s. critelli Fig. 3. Generalized map of the southern Peri-Tyrrhenian region, from Sardinia-Corsica to the Apulia. Modified after Critelli and Le Pera (1998). Tyrrhenian Margin). The modern setting includes two different styles of basins, A) the Corigliano Basin, on the Ionian side, a wedge-top depozone, located above thrust-sheets of the Calabrian Arc and southern Apennines terranes, and B) the Paola basin, on the Tyrrhenian side, a slope basin located on the eastern margin of the Tyrrhenian backarc basin (figs. 3, 4). Depositional Zones and Geometries. The Clastic infill of Foreland Basin Systems In foreland settings, subsidence and uplift are profoundly affected by lithospheric flexure. Foreland basin subsidence is primarily controlled by downflexing of the lithosphere in response to thrust loading (e.g. Jordan, 1981, 1995; Beaumont, 1981). Subsidence rate gradually decreases away from the thrust front producing an asymmetrical depression. Flexure uplift (forebulge) occurs as an isostatic response to downwarping and forms the distal margin of the foreland basin. Cratonward of the forebulge flexure, a broad shallow downwarp or intrashelf basin forms, the back-bulge basin (fig. 1; e.g. Quinlan and Beaumont, 1984; DeCelles and Giles, 1996).

7 the interplay of lithospheric flexure and thrust accomodation ::: 263 Fig. 4. Chart showing major Mesozoic-Cenozoic tectonic and depositional events in southern Italy sedimentary assemblages. Modified after Critelli and Le Pera (1995a) and Critelli et al. (1995b). The dimension and amount of flexural subsidence and uplift produced by the flexural features (i.e., foreland basin, forebulge, back-bulge basin) primarily depend on the geometry and density of the tectonic load, rheology of the lithosphere, density and volume of the sediment infill, and amount of thrust wedge and forebulge erosion (e.g.

8 264 s. critelli Beaumont, 1981; Jordan, 1981; Vai, 1987; DeCelles and Giles, 1996; Sgrosso, 1998). East or northeast-dipping subductions generate thrust-belt having high-rilief, and shallow foreland basins having low subsidence rates; in contrast, west-dipping subductions generate thrust-belt having low relief, and deep foreland basins having high subsidence rates (e.g. Doglioni, 1994). The interrelationships between lithospheric flexure, single thrust accomodation within the accretionary wedge and flexural subsidence experiences geometrically complexes entities within the foreland region. The foreland basin system may be divided into four depozones, the wedge-top, the foredeep, the forebulge, and the back-bulge depozones (fig. 1; e.g. DeCelles and Giles, 1996). Boundary between depozones may shift laterally through time following the deformation advancing. The longitudinal dimension of the foreland basin system is roughly equal to the length of the adjacent fold-thrust belt (e.g. DeCelles and Giles, 1996). Wedge-Top Depozone. Large amounts of syntectonic sediment cover the frontal part of the fold-thrust-belt. The sediment that accumulates on top of the frontal part of the orogenic wedge constitutes the wedge-top depozone. Its extent toward the foreland is defined as the limit of deformation associated with the frontal tip of the underlying orogenic wedge. The main distinguishing characteristics of wedge-top deposits are the abundance of progressive unconformities (e.g. Riba, 1976) and various types of growth structures (folds, faults, cleavages; Boyer and Elliot, 1982; Cello and Nur, 1988; Srivastava and Mitra, 1994; DeCelles and Giles, 1996; Zuppetta and Mazzoli, 1997). Aerially extensive aprons of alluvial sediment or shallow shelf deposits commonly drape the upper surface of the orogenic wedge during periods the wedge is not deforming in its frontal part, and large, long-lived feeder canyons may develop and fill in the interior parts of orogenic wedges (e.g. Ori et al., 1986; DeCelles and Giles, 1996). Sediments of the wedge-top depozone typically reflect the erosion and unroofing of the thrust-belt (e.g. Critelli and Le Pera, 1994, 1995a, 1998; Trop and Ridgway, 1997). Foredeep Depozone. It is the mass of sediment that accumulates between the frontal tip of the orogenic wedge and the forebulge. Foredeeps are typically km wide and 2-8 km thick (e.g. DeCelles and Giles, 1996). Sediment is derived predominantly from the fold-thrust-belt, with minor contributions from the forebulge and craton (e.g. Schwab, 1986; DeCelles and Hertel, 1989; Critelli and Ingersoll, 1994; Critelli and Le Pera, 1998). Subaerial foredeeps receive sediment from both longitudinally and transversely flowing fluvial and alluvial deposystems, and subaqueous foredeeps are occupied by shallow lacustrine or marine deposystems that range from deltaic to shallow shelf to turbidite fans. Foredeep depozones have frequently recorded transitions from early deep-marine sedimentation («Flysch») to late coarse-grained, nonmarine and shallowmarine sedimentation «Molasse» (e.g. Covey, 1986; Crook, 1989; Sinclair and Allen, 1992). The transition from «Flysch» to «Molasse» most likely reflects the fact that foreland basin systems originate as oceanic trenches (or remnant ocean basin) and later become shallow marine or nonmarine as continental crust enters the subduction zone (e.g. Ingersoll et al., 1995; DeCelles and Giles, 1996).

9 the interplay of lithospheric flexure and thrust accomodation ::: 265 Forebulge Depozone. It consists of the region of potential flexure uplift along the craton side of the foredeep. Because of forebulge depozone is a positive, and potentially migratory, feature, which may be eroded, its potential of preservation is low. One signal of the presence of an ancient forebulge may be the erosional unconformity surface. The forebulge generally is considered to be a zone of nondeposition or erosion, and the resulting unconformity may be used to track its position through time (e.g. Vai, 1987; Bosellini, 1989; Crampton and Allen, 1995; DeCelles and Giles, 1996; Sgrosso, 1998). In subaerial foreland basin systems (in which foredeep is not filled to the crest of forebulge) the forebulge may be a zone of erosion, with streams draining both toward and away from the orogenic belt (Crampton and Allen, 1995). If sediment derived from thrust-belt progrades into the forebulge, a thin condensed fluvial and aeolian sediment is deposited (DeCelles and Giles, 1996). In subaqueous foreland basin systems (in which foredeep is not filled up to the crest of forebulge), local carbonate platforms may develop in the forebulge depozone; extensive forebulge carbonate platforms and ramps can connect the foredeep with the back-bulge depozone (Giles and Dickinson, 1995). Back-bulge Depozone. It constitutes the sediment that accumulates between the forebulge depozone and the craton. Sediment contributions from the craton and development of carbonate platforms may be significant in submarine systems (e.g., DeCelles and Giles, 1996). Stratigraphic units in the back-bulge are generally much thinner than those in the foredeep, and consist of dominantly shallow-marine and nonmarine sediments. Sediment Compositions of Clastic Units. Lithologic Provenance Models. Foreland regions are one of the typical setting in which huge volumes of clastic sediments are rapidly accumulated. Provenance studies in this tectonic setting have long been used to contribute the complex history of the basin evolution, sediment dispersal pathways, dating major thrust events, and the unroofing history of the thrust-belt (e.g. Wiltschko and Dorr, 1983; Graham et al., 1986; Dickinson, 1988; Jordan et al., 1988; Steidtmann and Schmitt, 1988). Tectogenic sediments may be shed as alluvial fans in front of rising thrust sheets, and the age of these sediments may indicate the time of motion on some faults. In this setting, the uplift-erosion-transport-deposition system are genetically and intimately related to the style of deformation in thin-skinned, thrusted terrains. Transport of clastic sediment in the same direction as tectonic transport is the commonly assumed setting for the clastic-wedge/thrust association (e.g. Graham et al., 1986; Jordan et al., 1988; Steidtmann and Schmitt, 1988), that is named as «synthetic dispersal». However, opposite sediment dispersal pathways with rispect the tectonic transport is named as «anthitetic dispersal» (e.g. Steidtmann and Schmitt, 1988). The results is that sediment dispersal pathways in foreland basin systems are controlled by geometries within the thrust-sheet system, as frontal ramps, lateral ramps, diverse hanging-wall beds dip.

10 266 s. critelli In settings where distinct source-rock compositions are eroded sequentially, as in the case of predominantly vertical uplift of a stratigraphic section, «unroofing sequences» are commonly formed in the resultant clastic wedge (e.g. Graham et al., 1986; DeCelles, 1988; Steidtmann and Schmitt, 1988). This erosional inverted clast stratigraphy can provide valuable information about the evolving source and the identification of specific source areas (e.g. DeCelles, 1988; Colombo, 1994; Critelli and Ingersoll, 1994; Critelli et al., 1995a; Critelli and Le Pera, 1998). In the case of thin-skinned thrusted terrains (where horizontal transport dominates), layered rocks having different lithologies are exposed to erosion as they pass over a ramp providing a blended clastic dispersal of the exposed rock types. The resulting clastics may show no unroofing sequences, but include the same blended clast composition for relatively great thickness. These blended clastics may indicate that the source rocks were formed by tectonic transport over a ramp (e.g. Steidtmann and Schmitt, 1988). In thin-skinned thrust belts, both «unroofing sequences» and «blended clastics» can result in combinations. Large and Regional-Scale Models based on Sand(stone) Petrofacies. Numerous studies have demonstrated that sand (stone) from foreland basins are characterized by high framework percentages of quartz and unstable sedimentary and metamorphic lithic fragments, and the mean composition is quartzolithic (e.g. Dickinson, 1985, 1988; Schwab, 1986; DeCelles and Hertel, 1989; Critelli and Ingersoll, 1994). These studies provide a basis for interpretations of tectonic setting from sand (stone) composition. Sandstone petrofacies can be considered a reliable general guide to the overall tectonic settings of most sediment provenances; and although many processes may modify the composition of sedimentary detritus, the fundamental imprint of provenance tectonics is preserved in the final sedimentary products. The key petrofacies of various sedimentary basins occur most typically when transport is short and direct. In other cases sandstone petrofacies in many sedimentary basins have multiple sources showing complex paleotectonic and paleogeographic relationships to the basins (e.g. Dickinson, 1988). The foreland basin systems are a typical basin-setting in which multiple sources can be active in the same time, and the derivative sandstones may show mixed petrofacies (fig. 5; Dickinson et al., 1986; Schwab, 1986; Critelli and Le Pera, 1998). Schwab (1986) in a general statement of foreland-basin sandstone petrofacies testifies the complex pattern of provenance relationships during the foreland basin evolution. Quartzose sand is typical during the early stage of foreland infill, where the thrust-belt has low elevation and consequently supplies low amounts, whereas cratonal region is flexing and supplies more amounts (Dickinson et al., 1986; Cazzola and Critelli, 1987). Subsequent petrofacies is typical quartzolithic, when the thrust-belt is growing. Local provenances from magmatic arcs, uplifted subduction complexes or uplifted carbonate rocks of the forebulge only represent small amounts of the clastic record within foreland basin system. If thrust belt has severe uplift exposing the crustal basement, petrofacies can evolve to quartzofeldspathic sand (e.g. Critelli and Ingersoll, 1994; Garzanti et al., 1996; Critelli and Le Pera, 1998; Critelli and Reed, 1999).

11 the interplay of lithospheric flexure and thrust accomodation ::: 267 Fig. 5. QmFLt (Qm = monocrystalline quartz, F = feldspars, Lt = aphanitic lithic fragments) diagram to illustrate concept of mixing detritus from different provenance types to produce detrital modes reflecting mixed provenance (from Dickinson, 1988). Typical foreland-basin sand suites were derived from uplifted fold-thrust belts exposing sedimentary and metasedimentary strata. The mixed provenance relations are also typical of some foreland basin systems and remnant ocean basins (i.e. southern Apennines foreland, Indus and Bengal fans of the Himalayan belt). During early stage of foreland infill, sand may derive from cratonal areas, generating quartzose sand. Subsequent petrofacies is quartzolithic, and during final foreland infill, petrofacies may be mixed and quartzofeldspathic. Foreland sandstone detrital modes reference data plotted are: the modern Amazonian foreland (open square; data from DeCelles and Hertel, 1989), the Himalayan foreland [Siwalik (filled triangle) and modern rivers (open triangle); data from Critelli and Ingersoll, 1994], the Bengal and Indus Fan (polygons; data from Garzanti et al., 1996), and the southern Apennines foreland (filled and open circles for Miocene sandstone, and polygon for Holocene Crati Fan; data from Critelli and Le Pera, 1994, 1995a). The arrows, symbols (filled triangle and square) and specific fields within the diagram show the sand suite trends from different generic types of provenance terranes (e.g. Dickinson, 1985, 1988). Southern Italy and environs: structure and evolution The study area is a transect across the Calabria block and Apulia platform (figs. 6, 7). The transect across the northern Calabria, calabro-lucanian boundary, the Campanian and Lucanian ranges, the Bradanic basin and Apulia foreland exposes all ages of rocks from lower Paleozoic to Quaternary. These rocks experienced a large series of geodynamic events, that are: (1) early to middle Paleozoic orogenesis, (2) Hercynian orogenesis and plutonism, (3) Pangean breakup; (4) Tethyan rifting and subsequent oceanization; (5) Alpine deformation; (6) oceanic subduction and related subduction complex, accretionary wedge, and arc-volcanism; (7) Apennine accretionary processes

12 268 s. critelli Fig. 6. Geographic sketch map showing localities cited in the text. on Adriatic-Ionian lithosphere, related to roll-back of the subduction plane; (8) Backarc rifting (Tyrrhenian Sea); (9) Backarc oceanization, and deformation and dissection of the Apenninic accretionary wedge and Adria.

13 the interplay of lithospheric flexure and thrust accomodation ::: 269 Fig. 7. Geological sketch map of the main tectonostratigraphic units of the Southern Apennines (A) and the Calabria-Peloritani Arc (B). A] 1) Lower Messinian to Holocene sediments (a: Monte Vulture volcanic and volcaniclastic rocks); 2) San Bartolomeo Formation (Messinian); 3) Castelvetere, Oriolo, Monte Sacro, Nocara, Serra Manganile formations (upper Tortonian to lower Messinian); 4) Gorgoglione Formation (Tortonian); 5) Piaggine Formation (Serravallian to Tortonian); 6) Serra Palazzo Formation (Langhian to Tortonian); 7) Cilento Group (Langhian to Tortonian); 8) Numidian Sandstone Formation (Langhian); 9) Liguride Complex (Cretaceous to early Miocene; a: Saraceno Formation); 10) Sicilide Complex (Jurassic to early Miocene; a: Albanella, Corleto, Colle Cappella, Tufiti di Tusa formations); 11) Shallow-water to deep-water carbonate units (Triassic to middle Miocene); 12) Deep-water pelagic sediments (Triassic to early Miocene; Lagonegro, Molise, Sannio units). B] 1) Pliocene to Holocene sediments and recent volcanic deposits; 2) Upper Tortonian to Messinian sediments; 3) Stilo-Capo d Orlando Formation (early Miocene); 4) Longobucco Group (Jurassic); 5) Jurassic to Cretaceous Ophiolitiferous units, and Paleozoic metamorphic and plutonic units; 6) Maghrebian units (Mesozoic to Tertiary); 7) Paludi Formation (Late Oligocene to early Miocene); 8) Frazzanò Formation (Oligocene to early Miocene). Modified after Critelli et al. (1995b). Present-Day Morphotectonic Zones, Foreland Basin System and Environs. The Apennines and northern Calabria are associated with the Tyrrhenian backarc basin. The Apennines have a deep foredeep and they are composed mainly of thrust sheets of sedimentary cover, with the metamorphic basement slices interpreted as

14 270 s. critelli Fig. 8. Cross sections from the Adriatic Sea to the Tyrrhenian Sea, crossing the main depozones of the modern southern Apennines foreland basin system; locations of the cross sections are in a). b) Cross section from the Paola Basin to the eastern Apulia, showing the Paola slope basin (Eastern Tyrrhenian margin), the Calabrian thrust-belt (orogenic wedge), the southern Apennines foreland region (wedge-top and foredeep basins) and the flexed Apulia foreland [Modified after Cello et al. (1981), and Pescatore and Senatore (1986)]. c) Cross section from the outer thrust front of the southern Apennines orogenic wedge to the southern Adriatic Sea; locations of the modern subaerial foredeep (Bradanic trough), forebulge (Murge), and back-bulge (southern Adriatic Sea) depozones are shown [Modified after Ricchetti (1980), and Ricchetti and Mongelli (1980)]. d ) General schematic deep cross-section of the southern Apennines orogenic wedge showing formation of the Puglia bulge. During middle Pleistocene, the Bradanic trough was inverted from subsidence to uplift. Modified after Doglioni et al. (1994). «Alpine» relicts, and outcropping only in the internal western parts (fig. 8). The northern Calabria is a relict of Alpine and pre-alpine basement thrusted up the Apennine pile. From south to north the southern Italy are subdivide into the following morphotectonic belts (Ippolito et al., 1975): (1) The northern Calabrian Arc, including ophiolites, crystalline basement rocks and Mesozoic sedimentary sequences; (2) the Cilento and Calabro-Lucanian Ranges, having ophiolitic, metasedimentary and sedimentary rocks. The Ranges include a Paleogene Subduction Complex (the Calabro-Lucanian Flysch Unit or Liguride Complex of southern Italy), the middle Miocene foreland strata of the Cilento Group and younger sequences, and the Mesozoic to Miocene carbonate platform and slope (inner platform or Alburni-Cervati-Pollino Units and the Monti della Maddalena Unit); (3) the Campano-Lucanian Ranges, including Mesozoic to upper Miocene deep-sea sequences of the Lagonegro and Sicilide units, the outer platform

15 the interplay of lithospheric flexure and thrust accomodation ::: 271 sequences (Monte Alpi units), and the Miocene foreland strata; (4) the Lucanian-Apulia lowland, including the Pliocene to Quaternary foreland clastics; and (5) the Apulian Swell, a Mesozoic to Quaternary carbonate platform (external platform). The southern Apennine ranges are a Neogene and Quaternary thrust belt located in the hanging wall of a W-directed subduction which has been detected by sismicity and tomography (e.g. Spakman, 1989; Selvaggi and Chiarabba, 1995). The subduction has a back-arc basin to the west, the Tyrrhenian basin, partly floored by oceanic crust of Pliocene and Pleistocene age (e.g. Finetti and Del Ben, 1986). The subduction plane, as such as the southern Apennines and Calabrian accretionary prism, have migrated eastward or southeastward causing the roll-back of the subduction (e.g. Malinverno and Ryan, 1986; Royden et al., 1987; Doglioni, 1991; Gueguen et al., 1997, 1998). The roll-back of the subduction hinge (rate of hinge retreat is 6 cm/y; Royden et al., 1987; Patacca et al., 1993) to the front of the southern Apennines appears to have been slowed and buckled during the Late Pleistocene by the interference of the thick continental lithosphere of the Adria Plate (Apulian swell) at the front of the belt (e.g. Doglioni et al., 1994, 1996). The Apennines and northern Calabria are characterized by a frontal active accretionary wedge, below sea-level, whereas the main elevated ridge to the west is in uplift and extension instead. The modern basin configuration of this thrust belt is represented by the wedge-top depozone (Corigliano-Amendolara basins), the marine and subaerial foredeep depozone (Gulf of Taranto and the Bradano river basin, respectively), the forebulge (the Gallipoli basin) and the back-bulge (southern Adriatic Sea) (figs. 6, 8, 9; e.g. Critelli and Le Pera, 1998). On the frontal thrust belt, Pliocene and Pleistocene marine and nonmarine depositional systems were deposited within wedge-top and foredeep basins, the most important are the Bradanic Trough and the Sant Arcangelo, Ariano, Benevento, Ofanto basins (D Argenio et al., 1973; Casnedi et al., 1982; Casnedi, 1988; Hippolyte et al., 1994a; b; Pieri et al., 1996; Amore et al., 1998). The elevated ridges of southern Apennines and northern Calabria have been uplifted and cross-cut by normal faults and transcurrent faults (e.g. Amato et al., 1991; Catalano et al., 1993; Monaco et al., 1995; Cello and Mazzoli, 1999). Several Pliocene-Pleistocene grabens cross-cut the Apennines and northern Calabria thrust pile, the most important are Vallo di Diano, Val d Agri, Potenza Basin, Mercure Basin and Crati Basin (e.g. Turco et al., 1990; Cinque et al., 1993; Colella, 1994; Tortorici et al., 1995; Schiattarella, 1998; Tavarnelli and Pasqui, 1998). On the backarc area, particularly along the western Calabria borderland, similar fault-controlled Pliocene-Pleistocene basins (Tortorici et al., 1995), as such as the Paola Basin and Gioia Basin, represent the synrift troughs of the eastern Tyrrhenian margin (e.g. Savelli and Wezel, 1980; Barone et al., 1982; Sartori, 1982, 1990). The northern Calabria and Apennines have low elevation (average m) but a thick pile of synorogenic sediment accumulation (up to 10 km from Miocene to modern). Also, some calculations (Doglioni et al., 1996; Gueguen et al., 1998) show that the thickness of sedimentary strata in the Apennines exceed km, and the

16 272 s. critelli Fig. 9. Bathymetric and structural map of the Gulf of Taranto, which is the deep-marine part of the modern foreland basin system along the south-east side of the Apennines orogenic belt. The Corigliano basin represents the wedge-top depozone of the foreland region, in which the Crati Fan has been developing during the last 6000 y. Modified after Critelli and Le Pera (1998). entire crustal thickness is about 30 km, suggesting a delamination of the lithospheric mantle during Apenninic subduction (e.g. Channel and Mareschal, 1989; Doglioni et al., 1996). The different morphotectonic zones of the southern Italy have also diverse uplift rates calculated for the last 1 My. The Calabrian ranges is peculiar for their high uplift rates that are 1 mm yr 1 (e.g. Cosentino and Gliozzi, 1988; Sorriso-Valvo, 1993; Westaway, 1993), where the maximum uplift is toward the frontal part of the accretionary prism (Ionian side) (Cosentino and Gliozzi, 1988). Plate-Tectonic Evolution. Apart the Paleozoic history of the Calabrian Terranes, the rock units of the southern Italy mountain ranges experienced intense history of rifting, drifting and subduction of oceanic and continental lithosphere occurred in the western Mediterranean region since early Mesozoic (e.g. Smith, 1971; Dewey et al., 1973, 1989; Biju-Duval et al., 1977; Cohen, 1980; Dercourt et al., 1986; Malinverno and Ryan, 1986; Bortolotti et al., 1990; Stampfli and Marchant, 1997; Gueguen et al., 1998). Rifting processes started during the early Mesozoic (fig. 10), developing shallow-water and deep-water sedimentation, evolving since middle Jurassic to oceanic basin (fig. 11; Piemont-Ligurian basin; e.g. Scandone, 1975; Dercourt et al., 1986; Vai, 1992; Stampfli and Marchant, 1997). The

17 the interplay of lithospheric flexure and thrust accomodation ::: 273 oceanic basin was closed at the end of the Cretaceous and continental collision affect the western Mediterranean region. Only remnants of oceanic lithosphere persist until the Paleogene-Neogene boundary (e.g. Knott, 1987, 1988; Dewey et al., 1989; Critelli, 1993; Monaco and Tortorici, 1995). The key geodynamic events into the Mediterranean region can be summarized as follow: a) Alate Paleozoic rifting and oceanisation of the eastern Mediterranean basin and a late closure of the Paleotethys (late Permian to Triassic) on a Greek and Turkish transect of the Tethyan realm (e.g. Stampfli and Marchant, 1997, and bibliography therein). This late Paleozoic rifting is usually regarded as post-collisional, even if it is often associated with calcalkaline volcanism or plutonism (e.g. Winterer and Bosellini, 1981). As regard the units of the southern Italy, thermal events affected the Calabrian terranes producing emplacement of plutonics ( Ma; Carboniferous-Permian boundary; Rottura et al., 1990; Ayuso et al., 1994) and thermal metamorphism (e.g. Acquafredda et al., 1994). The Permian rifting and volcanism is well known in the southern Alps (e.g. Winterer and Bosellini, 1981). b) The Neotethys rifting started during Triassic, separing Pelagonian and Pindos domains in the eastern Mediterranean. Triassic rifting fragmented the western Mediterranean, and the geopuzzle included the Iberian, Apulia, Eurasia, Africa, Hellenic-Turkey plates and the Austroalpine-Carpathian, Pelagonian microplates (fig. 10; e.g. Stampfli and Marchant, 1997, and bibliography therein). In southern Italy, the Triassic rifting is responsible for opening of the Lagonegro basin, and their basinal and marginal (San Donato Unit, inner platform, the Alburno-Cervati-Pollino-Panormide, and the Apulia platform) sedimentation (e.g. Grandjacquet, 1963; Scandone, 1967, 1975; Ogniben, 1969; Bernoulli and Jenkins, 1974; D Argenio, 1974; Ippolito et al., 1975; Channel et al., 1979; Mostardini and Merlini, 1986; Sgrosso, 1994; Marsella et al., 1995). At the Triassic-Jurassic boundary, the Calabrian crystalline terranes are unconformably covered by continental quartzarenite redbeds, followed by Jurassic shallow-water, slope and basinal carbonate and siliciclastic sediments (cf. Zuffa et al., 1980; Santantonio and Teale, 1987). c) The Jurassic Tethys Ocean is responsible for fragmentation of the major blocks on both eastern and western Mediterranean (figs. 10, 11). The Ionian Sea (a southern extension of the Lagonegro-Sicanian basin), a possibly pre-middle Jurassic oceanic basin (Finetti, 1985), represents the connection between the eastern Mediterranean and the transform ocean north of Africa. Jurassic ophiolite sequences crop out discontinuously in northern Calabrian arc and Lucania (Lanzafame et al., 1979; Beccaluva et al., 1982), and basinal and shelfal sedimentation is widespread on the Apulia plate (future Apenninic domain). The inner carbonate platform (Alburno-Cervati-Pollino-Panormide) has thick Jurassic and Cretaceous strata, as such as the outer carbonate platform (the Apulia platform) (e.g. D Argenio, 1974). The inner platform has a series of hiatus, at the Triassic-Jurassic boundary (Monti della Maddalena and San Donato Units), during Middle-Late Jurassic (Monti della Maddalena Unit), whereas the outer platform has a main hiatus at the Early-Late Cretaceous boundary (Monte Alpi Unit) and at the

18 274 s. critelli Fig. 10. Middle Liassic reconstruction of the Mesogean/Alpine regions. The sketch shows the Liassic rift, the older rift stages (late Paleozoic, and the Triassic rift), microplates dispersal, the nascent Neotethys Ocean, and active and inactive spreading ridges and arc-accretionary prisms. Lo = Lombardian basin; La = Lagonegro basin. Modified and simplified from Stampfli and Marchant (1997). Cretaceous-Paleogene boundary (Apulia platform) (D Argenio, 1974). These hiatus may be related to a thermal uplift phase related to the Tethys rifting. The Lagonegro and Sicilide basins are pelagic, and include cherty limestone, shale, argillaceous chert, marl, and resedimented carbonatoclastic gravity flows. These last carbonatoclastic strata seem to have a stratigraphic position related with the main hiatus of the carbonate platforms. Siliciclastic deposits are absent in the southern Italy paleogeographic domains; d ) The changing geodynamic nature from rifting to convergent occurred at the end of the Cretaceous and during the Paleogene. During the early Cretaceous, the Piemont Ocean terminates its spreading, and an incipient subduction produces the accretion of the Apulia Plate over the eastern margin of the Piemont Ocean. On the western side of the Piemont Ocean, an oceanic spreading generate the Valais Ocean Basin ( Ma) producing the definitive separation of the Iberian Plate (the Brianconnais, Corsica and Sardinia blocks) from the European Plate (e.g. Bortolotti et al., 1990; Stampfli and Marchant, 1997, and bibliography therein). The final closure of the Piemont Ocean and the Valais Ocean occurred in a span time from Early to Late Cretaceous. The remnant ocean basin between the Apulia Plate and the Brianconnais block was filled by siliciclastic turbiditic sequences, the Helminthoid Flysch (Antola, Cassio, Caio, Solignano formations) of the northern Apeninnes. These turbidite sandstone strata have

19 the interplay of lithospheric flexure and thrust accomodation ::: 275 Fig. 11. Jurassic/Cretaceous boundary reconstruction of the Mesogean/Alpine regions. Major plate rearrangement, with isolation of the Iberia plate, and the stop of the spreading of the Alpine Tethys (Ligurian [Li]-Piemont[Pi]-Penninic[Pe] Ocean). Va = Valais Ocean. Modified and simplified from Stampfli and Marchant (1997). quartzofeldspathic and quartzolithic compositions reflecting provenances from granitic, medium-to-low grade metamorphic and carbonate source rocks (Fontana et al., 1994). The inferred provenance suggested by occurrence of certain heavy minerals (staurolite and staurolite+chloritoide) is from austroalpine belt (Orobic Alps; Bernoulli and Winkler, 1990). The Cretaceous of the Southern Italy pelagic basins is dominantly represented by clay, marl and shale, pelagic carbonate and cherty limestone, and by resedimented coarse-grained carbonatoclastic turbidites and gravity flows into the Liguride, Lagonegro and Sicilide-Molise basins. The Cretaceous of the southern Italy carbonate platforms is well developed and is very thick, about 1000 m in the Alburno-Cervati-Pollino, and 2000 m in the Apulia platform. e) From the end of the Cretaceous to early Eocene, the European plate was progressively flexed by subduction and by overriding of the prograding orogen, causing an uplift of the European forebulge above sea level and thus significant erosion of the European platform accompanied by «flysch» deposits since Maastrichtian. The Eocene to early Oligocene Mesoalpine tectonic phase corresponds with the NW thrusting of the Adria plate over the European plate, producing a NW vergent folds and thrusts in the Alps (e.g. Stampfly and Marchant, 1997). The response of the Mesoalpine

20 276 s. critelli phase is the continental collision, and foreland basin systems were developed in the Alps. During Lutetian the European forebulge abruptly subsided (Allen et al., 1991) as a consequence of flexuration in response of the thrust load of the accreted Adria plate. The Mesoalpine tectonic phase caused regional metamorphism at around 38 Ma (e.g. Steck and Hunziker, 1994), and intra-orogenic magmatism along the Periadriatic zone. The Middle Oligocene (32-30 Ma) is characterized by intense magmatic activity, part of which is directly linked to the Algero-Provencal rift (Provence and Sardinia), part along the Insubric line and part along the periadriatic domain. In the Alps and northern Apennines, the Eocene and Oligocene siliciclastic sedimentary sequences record the main events of this portion of the Mediterranean geodynamics, with provenances from (a) Iberic plate (Corsica-Sardinia-Brianconnais), (b) Adria plate (austroalpine domain), (c) European plate, (d ) syneruptive magmatic activity, and from (e) both European and Adria forebulges. Sandstone strata of Helvetic flyschs and Molasse (Schwab, 1981, 1986), and of the Ligurian and subligurian domains testify the large variabilities of petrofacies (e.g. Valloni and Zuffa, 1984). In the southern Italy domain, the Calabro-Lucanian Flysch Unit and the Sicilide Complex strata represent deposition in remnant ocean basin related to the western subduction of the Adria oceanic lithosphere beneath the Iberia plate (fig. 12; e.g. Knott, 1988; Dewey et al., 1989; Critelli, 1993; Guerrera et al., 1993; Critelli and Le Pera, 1998). The subduction has been active for all the Paleogene and lower Miocene, producing an accretionary prism, the Calabro-Lucanian Flysch Unit and the Sicilide p.p. Complex, and a diffuse calcalkaline volcanism in Sardinia. The Calabro-Lucanian Flysch Unit records the accretionary processes along the Adria margin and the consumption of the oceanic crust. The Mesoalpine (Eocene to early Oligocene) tectonic phase in southern Italy corresponds with the subduction of the Adria-Ionian oceanic lithosphere beneath the Iberia plate (fig. 12). Clastics within the Calabro-Lucanian Flysch Unit (Critelli, 1993; Monaco and Tortorici, 1995) records the onset of the volcanic-arc activity of Sardinia, the assembled and deformation of the oceanic lithosphere within the subduction complex, and the progressive accretion of the Calabrian crustal terranes of the Iberia plate over the Adria and Africa margins (Dewey et al., 1989; Ben Avraham et al., 1990; Gueguen et al., 1998; Cello and Mazzoli, 1999). At the Eocene-Oligocene boundary, the mesoalpine phase along the Adria plate, is responsible for the initial flexure, a general erosional processes of both the inner platform (Alburni-Cervati-Pollino-Bulgheria; Boni, 1974; D Argenio, 1974) and outer platform (Monte Alpi-Apulia). f ) During early (fig. 12) to middle (fig. 13) Miocene the Apenninic domain is the place where immense volume of turbiditic sedimentation is in response of E-NE accretionary processes along the Adria plate (e.g. Ricci Lucchi, 1986; Patacca and Scandone, 1987; Boccaletti et al., 1990). In the southern transect of the Apenninic domain, there are direct relations between crustal block source areas (the Calabrian Arc) and depositional sequences (foreland turbiditic clastic wedges). Here, the foreland basin system is developed over deformed Liguride Complex, during the early-middle Miocene, over Sicilide, Lagonegro and inner platform units during the upper Miocene

21 the interplay of lithospheric flexure and thrust accomodation ::: 277 Fig. 12. Paleogeographic reconstructions (Oligocene to early Miocene) of the western Mediterranean during progressive closure of the remnant ocean basin and onset of collision in southern Apennines. Modified after Dewey et al. (1989) and Critelli (1993). (fig. 14), and over the previous units and the western margin of the Apulia platform during the Pliocene to Quaternary. The time-progressive accretionary processes along the Adria plate is responsible for the intense lithospheric flexure of the Adria plate. The foreland basin system (wedge-top, foredeep, forebulge, back-bulge depozones) migrated in time, and siliciclastic and carbonatoclastic deposits, filling the wedge-top and the foredeep, where derived from progressive unroofing of the Calabrian crustal block or from erosion of the forebulge (e.g. Critelli and Le Pera, 1998). g) The geodynamic events of the last 10 My, in the western-central Mediterranean

22 278 s. critelli Fig. 13. Palinspastic restoration of the Apenninic domains during Langhian. Modified after Patacca et al. (1992). is named the Tyrrhenian phase (15-0 Ma) (fig. 14). The Tyrrhenian phase (or back-arc extension) is responsible for the fragmention and dispersion of pieces of the Iberian and European plates (Calabria, Sardinia, Corsica), increased the displacement of the accretionary prism over the Adria plate, the eastward migration of the magmatic arcs, and the roll-back of the Adriatic lithosphere (Malinverno and Ryan, 1986; Patacca et al., 1990, 1993; Argnani et al., 1995; Doglioni et al., 1996; Gueguen et al., 1997, 1998). The Tyrrhenian backarc basin migrated eastward (northeastward in the northern Apennines and southeastward in Calabria and Sicily) at velocities of up to 5-7 cm/yr in the most arcuate parts of the arc (Doglioni, 1991; Gueguen et al., 1998). Structural Evolution and Rise of the Calabrian Terranes. The Calabrian terranes form an arcuate mountain belt that lies between the thrust belts of the Apennines to the north and the Maghrebides to the west (fig. 3). The Calabrian terranes comprise nappes of Jurassic-Cretaceous ophiolitic sequences, and Hercynian and pre-hercynian continental basement rocks (fig. 15) that are in part affected by varying grades of later Alpine retrograde metamorphism (Amodio Morelli et al., 1976; Atzori et al., 1984; Del Moro et al., 1986; Messina et al., 1994). The Paleozoic metamorphic and plutonic terranes of the Calabrian Arc represent the remnants of

23 the interplay of lithospheric flexure and thrust accomodation ::: 279 Fig. 14. Palinspastic restoration of the Apenninic domains during the late Tortonian to early Messinian (time interval 8-6 my). Initial back-arc rifting of the Tyrrhenian Sea, and diverse wedge-top and foredeep depozones in the southern Apennine foreland region. Modified after Patacca et al. (1990). Caledonian, Hercynian and Alpine orogens (e.g. Amodio Morelli et al., 1976; Schenk, 1981; Zanettin Lorenzoni, 1982; Atzori et al., 1984; Del Moro et al., 1986; Zeck, 1990; Messina et al., 1994), that are drifted from the southern Iberic plate and accreted since upper Oligocene over the Adria-Africa lithosphere. They are a key tectonic element of the southern Italy orogen. Erosional remnants of the Calabrian Arc terranes occupy a belt that is presently as much as 75 km wide in northern Calabria. Here, the arc can be divided into three stacked tectonostratigraphic assemblages (figs. 15, 16; e.g. Amodio Morelli et al., 1976; Bonardi et al., 1976; Scandone, 1979, 1982; Cello et al., 1981; Bonardi et al., 1982; Colonna and Compagnoni, 1982; Colonna, 1998). The lowest is composed of mainly carbonate rocks of Mesozoic age (D Argenio et al., 1973; Ietto and Barillaro, 1993; Iannace et al., 1995; Perrone, 1996; Ietto and Ietto, 1998) that were originally deposited on the continental margins of the Apulia/Adria plate (Channel et al., 1979). These sediments were stripped from their basement during the early Miocene collision of Calabria with Africa and Adria, and now form part of the Africa-verging Apennine fold-thrust belt. The middle tectonic units are composed of two nappes (Diamante- Terranova-Grimigliano and Malvito units; fig. 16) of Mesozoic metasedimentary and ophiolitic rocks, which can be interpreted as the remains of the neo-tethyan Ocean

24 280 s. critelli Fig. 15. Tectonic sketch map of the Calabria-Peloritani Arc. 1) Pliocene to Holocene sediments, and volcanic and volcaniclastic rocks; 2) Upper Tortonian to Messinian clastics and evaporites; 3) Cilento Group (Middle Miocene); 4) San Donato, Verbicaro and Pollino Units (Triassic to Miocene); 5) to 7) Liguride Complex: 5. Calabro-Lucanian Flysch Unit (Upper Jurassic to Upper Oligocene); 6. Ophiolitiferous blocks and Mèlange; 7. Frido Unit (Upper Jurassic to Upper Oligocene); 8) Longobucco and Caloveto Groups (Lower Lias to Lower Cretaceous) and Paludi Formation (Upper Oligocene); 9) Sila, Castagna and Bagni basement Units (Paleozoic); 10) Malvito, Diamante-Terranova, Gimigliano Ophiolitiferous units (upper Jurassic to Lower Cretaceous); 11) Floresta Calcarenite (Middle Miocene), Stilo-Capo d Orlando Formation (Lower Miocene); 12-13) Stilo Unit: 12. Carbonate rocks of the Stilo Unit (Upper Triassic? to Cretaceous) and 13. Basement rocks (Paleozoic); 14) Sedimentary Cover of the Longi-Taormina Unit (Upper Triassic to Oligocene); 15) Basement rocks (Paleozoic) of the Aspromonte, Africo, Mandanici, Fondachelli, Longi, Taormina units; 16) Sedimentary units of the Maghrebian Chain. Modified after Bonardi et al. (1993). (De Roever et al., 1974; Amodio Morelli et al., 1976; Lanzafame et al., 1979; Guerrera et al., 1993; Cello et al., 1996). The uppermost tectonic units consist of thrust

25 the interplay of lithospheric flexure and thrust accomodation ::: 281 Fig. 16. Sketch map of the Calabria-Peloritani Arc, showing the outcrop of the ophiolitiferous and crystalline basement rocks, and simplified tectonostratigraphic terranes of the northern Calabrian Arc. Simplified tectonostratigraphy of the nappe sequence is modified after Amodio Morelli et al. (1976). Data of Apatite and Zircon Fission-Track ages is from Thomson (1998). Data on fission-track ages of the key thrusted terranes constraints times of tectonic accomodation of the nappe piles. See Thomson (1998) for further details. sheets of Paleozoic igneous and metamorphic rocks (Bagni, Castagna and Sila units) and Mesozoic (Longobucco Group) to Cenozoic sediments (figs. 15, 16), considered to be the basement and cover, respectively of the former Iberian/Europe margin of Neotethys (e.g. Ogniben, 1969, 1973; Bouillin, 1984; Bouillin et al., 1986; Knott, 1987, 1988; Dietrich, 1988; Dewey et al., 1989; Thomson, 1998). However, other authors consider the Calabrian basement terranes as a part of the Austroalpine domain of the African

26 282 s. critelli Plate (e.g. Haccard et al., 1972; Alvarez et al., 1974; Alvarez, 1976; Amodio Morelli et al., 1976; Scandone, 1979, 1982; Bonardi et al., 1982, 1993; Dercourt et al., 1986). In other alternative interpretations, the nappes of the Calabrian Arc originated from a microcontinent located between the European and African continents (e.g. Wildi, 1983; Guerrera et al., 1993; Critelli and Le Pera, 1998) or the Calabrian-Arc terranes are the results of assembling three «crustal microblocks» (e.g. Vai, 1992). Fission tracks of the continental basement units of the northern Calabrian terranes constraints on the age of the tectonic contacts between the three stacked units of basement (fig. 16; e.g. Thomson, 1994, 1998). Thomson (1998) demonstrates that the emplacement of continental basement rocks with Alpine metamorphism over ophiolitic rocks is constrained as a thrust contact of lower-to-middle Miocene age (<23 Ma), and the other major thrust contacts of the diverse alpine basement units may be <18 Ma (fig. 16). The relative cooling ages range from 35 to 15 Ma based on apatite fission tracks, where most of this phase of accelerated cooling can be attributed to increased erosion (Thomson, 1994, 1998). The relevant results of apatite and zircon fission tracks from northern Calabria basement rocks are accomodation of thrust units since 23 Ma, and progressive exhumation since 23 Ma to about 10 Ma. This exhumation history is also reflected by clastic detrital modes related to the unroofing of the basement rocks of the northern Calabrian terranes (e.g. Critelli and Le Pera, 1994, 1995a; b, 1998). Since about 20 Ma immense volumes of Calabrian-derived clastic detritus have filled the sedimentary basins of the southern Apennine domain on both foreland and backarc regions. The high erosional rates ( mm y 1 )ofthe Calabrian Arc, that seems to be almost equal to the uplift rates ( mm y 1 ), experienced a very high sediment accumulation rates on borderland Ionian and peri-tyrrhenian basins (e.g. Wezel et al., 1981, 1982; Sartori, 1982; Wezel, 1982; Ibbeken and Schleyer, 1991; Kiefer, 1994). This recent (Pliocene-Quaternary) source/basin relationships and related processes represent an actualistic analogue of the Miocene processes during growth of the southern Italy orogenic system (e.g. Critelli and Le Pera, 1998). Mesozoic to Recent Clastic Sediments as Records of Tectonic Evolution. Clastic sediments are an important component within the southern Italy orogenic system. These sediments range in age since early Mesozoic (early Triassic to the present). Apart the Mesozoic and Paleogene clastics that are few or absent, and do not reflect an orogenic provenance, the major clastic contributions occur since Late Oligocene to the present (fig. 4; Carbone and Lentini, 1990; Patacca et al., 1990; Critelli et al., 1995b; Critelli and Le Pera, 1995a, 1998; Sgrosso, 1998). Tertiary (Oligocene to late Miocene) sediments of the southern Apennines and northern Calabria were deposited in diverse basins, remnant ocean basin (Liguride Complex), foreland basin systems, and intermontane basin (Tortonian-Messinian synrift basin of the western Calabria). The clastic sediments mainly reflect provenance from Calabrian basement rocks, testifying their unroofing histories and synthetic and antithetic sediment dispersal as thrusting accomodated the basement units. Additional sources included the active calcalkaline volcanic arcs, the uplifted subduction complex, and the Adria fore-

27 the interplay of lithospheric flexure and thrust accomodation ::: 283 bulges as growing orogen advanced over the Adria plate (e.g. Critelli and Le Pera, 1998) (figs ). The close relationships between fission tracks in basement rocks of the northern Calabria (cf. Thomson, 1994, 1998) and detrital mode evolution of the upper Oligocene to upper Miocene synorogenic clastics of northern Calabria and southern Apennines (cf. Critelli and Le Pera, 1998) testify that thrusting, uplift and synorogenic deposits are intimately connected during the accretion of the Calabrian Arc over the Adria plate margin. Sequential history of growing orogen in southern Italy and clastic sediments in space and time The mountain ranges of southern Italy consist of tectonically juxtaposed thrust belts belonging to different paleotectonic domains (figs. 2, 3). They are separated by three main tectonostratigraphic units: 1) the Calabrian Arc (Amodio Morelli et al., 1976), 2) the Liguride Complex (Ogniben, 1969) and 3) the Apulia/Adria domain (Channel et al., 1979). The Calabrian Arc consists of Paleozoic crystalline and ophiolitic units locally including Mesozoic to Cenozoic sedimentary cover. They may represent remnants of a Mesozoic to Paleogene European or Meso-Mediterranean continental margin (e.g. Bouillin et al., 1986; Knott, 1987; Dietrich, 1988; Dewey et al., 1989; Guerrera et al., 1993; Gueguen et al., 1998). The Liguride Complex is an ophiolite-bearing tectonic unit related to westward subduction of the lithosphere of the Neo-Tethys Ocean beneath the European margin (Knott, 1987; Monaco and Tortorici, 1995). The Liguride Complex of southern Italy (Calabro-Lucanian Flysch Unit, Frido Unit and Saraceno Formation) has been interpreted as the result of sequential closure of a Paleogene remnant ocean basin located between the Adria margin and Calabria-Corsica-Sardinia block (Knott, 1987; Critelli, 1993; Guerrera et al., 1993; Critelli and Le Pera, 1995a; Critelli et al., 1995b; Monaco and Tortorici, 1995). The Apulia/Adria domain represents the Adriatic-African continental margin, consisting of carbonate platforms and pelagic basins (Bernoulli and Jenkyns, 1974; Scandone et al., 1974; Channel et al., 1979) spanning from lower Mesozoic to lower Miocene. [According to Stampfli and Marchant (1997) we name Apulia for Mesozoic paleogeography and Adria for Tertiary geodynamics.] These carbonate and pelagic sediments have been covered, since early Miocene, by the deep-marine to terrestrial foreland clastic wedges related to the progressive lithospheric flexure of the Adria passive margin beneath the advancing thrust belt (Mostardini and Merlini, 1986; Royden et al., 1987; Casero et al., 1988; Moretti and Royden, 1988; Patacca et al., 1990; Roure et al., 1991; Hippolyte, 1992; Critelli and Le Pera, 1998; Sgrosso, 1998; Gueguen et al., 1998). The salient events of the southern Apennines orogeny were the accretion of the Calabrian Arc terranes during the Late Oligocene to Middle Miocene and thrusting of the Liguride Complex (Calabro-Lucanian Flysch Unit, Frido Unit and Saraceno Formation) onto the Adria margin. Initial eastward growing of the crustal terranes was in response of the counterclockwise rotation of the Calabria-Corsica-Sardinia block (e.g. Dewey et al., 1973, 1989; Cohen, 1980; Montigny et al., 1981; Scandone, 1982).

28 284 s. critelli Northwest-dipping subduction of the remnant oceanic crust was responsible for diffuse calcalkaline volcanism along the western side of Sardinia. Imbrication and thrusting toward the Adriatic foreland occurred after closure of the remnant ocean basin during the Burdigalian (e.g. Malinverno and Ryan, 1986; Knott, 1987; Dewey et al., 1989). A significant change in the tectonic evolution of the Apennines took place in the late Tortonian, when rifting occurred in the backarc region, the Tyrrhenian area (e.g. Patacca et al., 1990; Sartori, 1990). Continental convergence continued along the outer margin of Adria, and a shift of the foredeep depozones toward the east-northeast occurred (e.g. Patacca et al., 1990, 1992). The present configuration of basinal sedimentation in the southern Italy results in an active foredeep basin, the Gulf of Taranto and related wedge-top depozone (i.e. Corigliano Basin; Pescatore and Senatore, 1986; Romagnoli and Gabbianelli, 1990), whereas the western margin of Calabria corresponds with the backarc region of the Tyrrhenian basin (i.e. Paola Slope Basin; Trincardi et al., 1995) (figs. 8, 9). Mesozoic Rifting Clastic Units (Triassic to early Cretaceous). Alboran Block. We include in the Alboran block, the Calabria, Betic Cordillera (Alpujarrides, Rondaides and Malaguides), Tellian Maghrebides (Grande and Petite Kabilies, Edough, Algers Massif) Rifain Sebtides, Tetuanides and Ghomarides (Wildi, 1983; Bouillin et al., 1986; Guerrera et al., 1993). Calabria is part of this block, and during the upper Triassic to early Jurassic (fig. 10), some of the basement units composing the Calabrian terranes have nonconformably siliciclastic redbeds. These are part of the Longi-Taormina, Longobucco (Zuffa, 1978; Zuffa et al., 1980) and Tiriolo (Critelli and Ferrini, 1988) units, and consist of fluvial to deltaic sandstone and conglomerate. Sandstones have quartzose (quartzarenite to sublitharenite) composition (fig. 17), and lithic detritus consists of low-grade metamorphic, felsic volcanics, and radiolarian chert, reflecting a provenance from climatically controlled low-grade metamorphic, volcanic and siliceous sedimentary source rocks. The low-grade metamorphic rocks are widely present and they represent also the basement of the redbeds itself, whereas the felsic volcanic rocks are rare in the Calabrian basement, but they are present in the Sardinia island, over the early to middle Paleozoic basement, that are Permian in age. Similar redbeds are in the Betic Cordillera units, where sandstones have the same composition and provenances of the Calabrian-Peloritani Arc redbeds (Critelli, Le Pera, Martin-Algarra and Perrone, unpublished data). Other similar redbeds are in the northern Africa units, but data on sediment composition are not available. The Upper Triassic-Lower Jurassic redbeds are covered by shelfal, slope and basin clastic and carbonate sediments (e.g. Zuffa et al., 1980; Santantonio and Teale, 1987). Sandstones are quartzarenitic to sublitharenite in composition, showing same local petrofacies (i.e. Longobucco Sequence; e.g. Zuffa et al., 1980), reflecting, with together the redbeds, a lowland climatically-controlled source area. Oceanic Basin. We include in the oceanic basin sediments covering the oceanic basement (fig. 11), nowely present in northern Calabria (Diamante-Terranova, Malvito

29 the interplay of lithospheric flexure and thrust accomodation ::: 285 Fig. 17. QtFL plot (with superposed provenance fields of Dickinson, 1985) summarizing sandstone compositions for Triassic to Cretaceous sedimentary assemblages of the southern Italy and southern Spain tectonostratigraphic units: (1) Early Triassic sandstones of the Monte Facito Formation (Lagonegro Basin), (2) Upper Triassic to Early Jurassic continental redbeds and Early to Middle Jurassic shallow-water to deepwater sandstones of the Calabria-Peloritani Arc (Longobucco, Tiriolo, Longi-Taormina units) and the Betic Cordillera, Spain, and (3) Jurassic to Cretaceous quartzose sandstones deposited within the Ocean basin (Liguride basin). Data for Longobucco Group are from Zuffa (1980), and Zuffa et al. (1980); data from Monte Facito Formation, redbeds of the Peloritani Mountains and Betic Cordillera are unpublished data. and Gimigliano units; Amodio Morelli et al., 1976) or assembled (as blocks and broken formations) within the Calabro-Lucanian Flysch Unit (Monaco et al., 1995). The oceanic basement is covered by red and green clays, argillaceous chert, radiolarian chert, local limestone, and quartzarenite turbidites (fig. 18). These quartzose turbidites are few strata and appearing since Middle Jurassic. Apulia Margin. Late Permian to early Triassic dominantly continental redbeds (sandstone, breccia, dark-red argillites) are present at the base of the Apulia platform, possibly overlying the Paleozoic basement (e.g. Mostardini and Merlini, 1986; Ricchetti et al., 1988). These redbeds, possibly several hundred of meters in thickness, are drilled (at 7070 m deep), in an exploration well (Puglia 1; cf. Ricchetti et al., 1988), and are described as quartzose to sublitharenite sandstones. The redbeds are overlain by, more than 1000 m in thickness, upper Triassic tidal-flat-sabka evaporitic limestone, dolostone, and anhydrite strata (Burano Formation), and by 5000 m of upper Neocomian-Lias (Ugento Dolomite), Cenomanian-upper Neocomian (Bari Limestone) shallow water carbonates.

30 286 s. critelli Fig. 18. Salient sedimentary events for the Liguride Complex of southern Italy. During oceanic rifting (Jurassic to Early-late Cretaceous), sedimentation within the ocean basin includes pelagic red and green clays, argillaceous chert, radiolarian chert, rare limestone, and quartzose (qz) turbidite sandstone (A;B = photomicrographs of a quartzarenite strata). During closure of the oceanic basin (? Late Cretaceous-early Miocene), sedimentation within the subduction complex includes a tectonic melange (Calabro-Lucanian Flysch Unit) having interbedded volcaniclastic (C; v = volcaniclastic strata) and quartzofeldspathic sandstone strata, recording climax of neovolcanic activity (D; syneruptive volcaniclastic strata; detritus includes basaltic and andesitic detritus; Lv = volcanic fragments), and accretion of oceanic lithosphere (producing abundant serpentinite [S] detritus; E). The Saraceno Formation represents the final infilling of the oceanic basin. The turbidite portions of the Saraceno Fm. (F; the outcrop is overturned) evolve from dominantly carbonatoclastic strata (calclithite, hybrid arenites, calcarenite (a) to mixed carbonate-metamorphic detritus (b), recording the first signal of the Calabrian Arc unroofing history. Lower-Upper Triassic (Scythian-Anisian to middle Carnian) sandstones are the base of the Lagonegro basin, named the Monte Facito Formation (e.g. Scandone, 1967). The formation is about 300 m in thickness, and consists of sandstone, marl, red clays, rare conglomerate, calcarenite and cherty limestone. Sandstone of the Monte Facito For-

31 the interplay of lithospheric flexure and thrust accomodation ::: 287 mation is described as quartzose sandstone (fig. 17; Scandone, 1967). Sediments of the Monte Facito Formation were interpreted as shallow-marine (Scandone, 1967), but siliciclastic strata and carbonate strata of the formation, could represent broken formations and olistholiths of a base of slope sequence (Wood, 1981; Marsella et al., 1991; Scandone, personal communication). These sediments include resedimented detritus having Permian foraminifera. The Monte Facito Formation is overlain by a thick Triassic to Miocene pelagic sequence, including the Cherty Limestone Formation (middle Carnian to Raethian, m in thickness), Radiolarite Formation or silicified argillite Formation (Raethian to Lias-Malm), The Galestri Formation (graded limestone, siliceous marlstone, calcarenite, and calcilutite; Upper Jurassic to Lower Cretaceous) (Scandone, 1967, 1972; Amodeo et al., 1991; Marsella et al., 1995). Pre-Collisional and Earliest Collisional Clastic Units (Late Cretaceous to early Miocene). This large time span corresponds with the main Alpine tectonic phases and final closures of the Piemont and Valais oceanic basin to the north, whereas in the southern Italy, a more external remnant oceanic basin, the Calabria-Lucanian oceanic basin, divides the Apulia/Adria margin from the Alboran Block (e.g. Channel and Mareschal, 1989; Dewey et al., 1989; Guerrera et al., 1993; Critelli and Le Pera, 1998). The Adria plate experienced abrupt surficial and lithospheric changes, as changing nature of the pelagic basins, onset of siliciclastic sedimentation, huge volumes of cratonic quartzose sediments, emersion and erosion of carbonate platform domains, and deformation of the inner carbonate platform to form a forebulge (Patacca et al., 1992; Sgrosso, 1998). The oceanic lithosphere was subducting beneath the Alboran-European plates, with the Calabria-Lucanian (Liguride) basin representing the oceanic accretionary wedge, and a diffuse calcalkaline volcanism was located in Sardinia. Alboran Block. During Paleogene to early Miocene, sediments over the Calabrian terranes include the Upper Oligocene to lower Miocene Frazzanò Formation (de Capoa et al., 1997), in the Peloritani sector of the arc, and the upper Oligocene to lower Miocene Paludi Formation (northern sector) and Stilo Capo d Orlando Formation (southern sector). These sandstones are quartzofeldspathic (fig. 19; Zuffa and De Rosa, 1978; Puglisi, 1987; Cavazza, 1989; Nigro and Puglisi, 1993; Critelli et al., 1995b) and reflect their local provenance from crystalline rocks of the Calabrian terranes. The tectonic setting of these basins is complex; the sequences suturing some crystalline thrust units could represent a wedge-top deposition on advancing calabrian thrust-belt (e.g. Weltje, 1992; Patacca et al., 1993; Wallis et al., 1993) or may represent deposition in a forearc setting (e.g. Cavazza et al., 1997). An alternative interpretation is that they could represent remnants of deposition in foreland setting related to the back-thrust belt of the Betics-Alps orogen (e.g. Doglioni et al., 1997; Gueguen et al., 1997, 1998). Possible remnants of a forearc basin successions can be the Troina-Tusa Formation (Wezel and Guerrera, 1973; Wezel, 1974, 1975, 1977) and Cerami Sandstone of the Reitano Formations (Grasso et al., 1978; La Manna et al., 1995), where their volcano-

32 288 s. critelli Fig. 19. QtFL plot (with superposed provenance fields of Dickinson, 1985) summarizing sandstone compositions from Paleogene to early Miocene sedimentary assemblages deposited during closure of the Liguride remnant ocean basin. Assemblages include the Calabro-Lucanian Flysch Unit (Tectonic Mélange) and the Saraceno Formation of the Liguride Complex (remnant-ocean basin), and episutural (forearc basin) assemblages of the Paludi, Frazzanò and Stilo-Capo d Orlando formations. Data from Liguride Complex are from Critelli (1993); data from Paludi, Frazzanò and Stilo-Capo d Orlando Formations are from Zuffa and De Rosa (1978), Puglisi (1987), Cavazza (1989), Nigro and Puglisi (1993). lithic, lithofeldspathic and quartzofeldspathic sandstones (Puglisi, 1987) are related to sudden input of volcaniclastic detritus from Sardina (Wezel, 1974, 1975, 1977) and from crystalline detritus of the southern Calabria terranes. Oceanic Area. During upper Cretaceous to early Miocene, the oceanic area experienced deformation and accretion, involving in a remnant ocean basin (Calabria-Lucanian basin; fig. 12). A tectonic melange (Calabro-Lucanian Flysch Unit; Spadea, 1982; Bonardi et al., 1988; Monaco et al., 1995) was formed in this time frame, including olistholiths and broken formations of oceanic sequences (both basement and its pelagic sedimentary cover) and crystalline rocks (gneiss and granite) (Spadea, 1982). The geodynamic scenario of this convergent margin setting includes the subduction of the Adria oceanic lithosphere beneath the European plate, producing along the southern-end of the European plate a continental-margin calcalkaline volcanic arc in Sardinia (e.g. Scandone, 1982; Malinverno and Ryan, 1986; Channel and Mareschal, 1989; Dewey et al., 1989). Cretaceous to Eocene quartzose sandstone (Crete Nere Formation; Bonardi et al., 1988), and late Paleogene (upper Eocene to upper Oligocene) quartzofeldspathic and volcanolithic sandstones are tectonically assembled within the tectonic mélange (Calabro- Lucanian Flysch; Monaco et al., 1995) (figs. 18, 19). Quartzofeldspathic sandstone was derived from mixtures of ophiolitiferous detritus and neovolcanic detritus. Syneruptive volcanolithic sandstones, having basaltic and andesitic fragments (fig. 18), reflect climax

33 the interplay of lithospheric flexure and thrust accomodation ::: 289 of activity of the Sardinia volcanic arc during its initial arc volcanism (late Oligocene, Ma; Critelli, 1993). The overlying sequence, the Saraceno Formation (that caps the Liguride Complex), is unconformably over the Calabro-Lucanian Flysch Unit, is mixture of siliciclastic and carbonatoclastic strata, that are hybrid arenites, lithic and quartzolithic sandstones (figs. 18, 19). These sandstones reflect a provenance evolution from sedimentary-dominant (both carbonate and siliciclastic fragments) detritus to metamorphic and sedimentary mixtures. This provenance evolution testifies the initial signal of accretion and unroofing of the frontal thrust system of the northern Calabrian terranes (Sila Unit; e.g. Messina et al., 1994). Apulia/Adria Margin. Siliciclastic sediments are rare or absent within basins located on Apulia/Adria continental crust. The paleogeographic scenario of this continental margin includes the outer carbonate domain (Apulia and Monte Alpi platforms), the Lagonegro basin, the inner carbonate platform, the Alburno-Cervati-Pollino platform and the Sannio and Sicilide p.p. basins (fig. 13). These paleogeographic domains are characterized by thick (several thousands of meters in thickness) carbonate platforms, and their slopes, and pelagic basins. The pelagic basins receive dominantly clays, marls and resedimented carbonate gravity flows (Patacca et al., 1992), Cretaceous to upper Oligocene in age. There are no important traces of siliciclastic turbidite sandstones in the Cretaceous-Oligocene stratigraphic interval; only rare quartzarenite strata are interbedded with siliceous clays (Pescatore et al., 1988). The carbonate platforms record repeated emersions during the Cretaceous (Albian, and Albian-Cenomanian; e.g. Carannante et al., 1988a), showing pervasive karsification and deposition of bauxite deposits (locally up to 10 m). The bauxite deposits seem to be related to an intense weathering of original fine volcanic deposits (Carannante et al., 1988a). The large emersion of the inner carbonate platform could be related to the onset of the deformational events along the Apulia margin and subsequent flexure of the forebulge (Carannante et al., 1988a). During Paleogene, carbonate platforms and their slopes are characterized by thin stratigraphic sections, repeated emersions and no deposition (hiatus) intervals, that include the Eocene-Oligocene in the Alburno-Cervati-Pollino Unit, all the Paleogene in the Monti della Maddalena Unit and Apulia platform Unit, and the Late Cretaceous to early Miocene in the Monte Alpi Unit (Marsella et al., 1995). Basinal sequences are dominantly pelagic, consisting of resedimented carbonate gravity flows (turbidite calcarenite to conglomerate debris flows and grain flows), representing carbonate slope aprons in the Lagonegro basin (Flysch Rosso Formation; Pescatore et al., 1988) and the Sicilide basin (Monte Sant Arcangelo Formation; Lentini, 1979), interbedded with siliceous clays and shales. Rare siliciclastic or hybrid arenites are in the Paleocene sections of the Sicilide Complex (Monte Sant Arcangelo Formation; Selli, 1962; Lentini, 1979). The sandstone is quartzolithic, including abundant quartz, and metamorphic and sedimentary lithic fragments. Eocene to Oligocene Colle Cappella Sandstone Formation (the lower portion of the Nocara Flysch; Ogniben, 1969; Zuppetta et al., 1984), is a turbidite system including abundant quartzolithic sandstones (Critelli and Le Pera, 1998). These sandstones have very abundant low-grade metamorphic fragments, sug-

34 290 s. critelli Fig. 20. QtFL plot (with superposed provenance fields of Dickinson, 1985) summarizing sandstone compositions from Burdigalian to Tortonian sedimentary assemblages deposited within the southern Apennines foreland basin system. Detrital modes of the Saraceno Formation shown as reference point of the onset of the unroofing history of the Calabrian terranes. The volcanic provenance from the volcanic arc is also recorded within the foreland basin sequences (Cilento Group and Sicilide Complex). Data from: Sicilide Complex is from Critelli et al. (1990, 1995b) and Fornelli and Piccarreta (1997); Cilento Group and Gorgoglione Formation is from Critelli and Le Pera (1994); Piaggine Sandstones and Serra Palazzo Formation is from Critelli and Le Pera (1995a). gesting initial erosion and accretion of the Calabrian terranes. However, the Colle Cappella Sandstone Formation could reasonable be younger than proposed ages, and be considered as early Miocene in age (Aquitanian to Burdigalian; figs. 12, 20) (Critelli et al., 1994, 1995b). During early Miocene an abrupt paleogeographic and geodynamic change occur along the Adria margin (figs. 12, 13). Transgressive shallow-water calcarenite sediments were deposited on carbonate platform domains (fig. 21; Selli, 1957; Carannante et al., 1988b; Patacca et al., 1992; Sgrosso, 1998). Within the Sicilide and Lagonegro basins a thick (up to 1000 m) quartzose turbidite sand, the Numidian Sandstone Formation (Patacca et al., 1992) represents the key signal of a mature quartzose (cratonic) provenance from the northern Africa continental margin (fig. 13; Wezel, 1970a; b; Patacca et al., 1992). This widespread quartzose material was deposited, during upper Burdigalian (?) to Langhian, within the nascent foredeep of the Sannio-Sicilide, on the forebulge of the Alburno-Cervati-Pollino platform, and on the back-bulge Lagonegro depozones (Patacca et al., 1992). Syneruptive andesitic volcaniclastic layers are interbedded with the shallow-water calcarenites (fig. 21), and quartzose sandstones testifying the volcanic activity on the Sardinia Arc (Patacca et al., 1992), as such as arkosic debris flows (cf. Carbone et al., 1987) recording signals of provenance from accreted crustal block of the Calabrian terranes.

35 the interplay of lithospheric flexure and thrust accomodation ::: 291 Fig. 21. Schematic columnar sections of the upper portions of the Adria carbonate platform domains, involved in flexural features during southern Apennines foreland basin system. The three sections correspond with the forebulge depozone sedimentation during (a) Burdigalian to early Tortonian (Alburno-Cervati-Pollino units or inner platform domain), (b) late Tortonian to Messinian (Monte Alpi unit), and (c) early Pliocene to the present (Apulia unit). Reference stratigraphic data for: the Alburno-Cervati-Pollino platform are from Carannante et al. (1988b), Critelli (1991), Patacca et al. (1992); the Monte Alpi Unit are from Sgrosso (1988), Taddei and Siano (1992), and personal unpublished data; the Apulia platform are from Ricchetti (1981), Ciaranfi et al. (1988), Ricchetti et al. (1988).

36 292 s. critelli The active volcanic source and the crystalline sources of the Calabria arc are recorded within the Sicilide foredeep, forming distinct early Miocene siliciclastic turbidite systems having sand compositions ranging from volcanolithic (Tufiti di Tusa Formation) to quartzolithic and quartzofeldspathic (Albanella, Corleto and Colle Cappella Formations) (fig. 20; e.g. Critelli et al., 1994; Fornelli and Piccarreta, 1997; Critelli and Le Pera, 1998). Volcaniclastic detritus, interbedded with quartzose sandstone strata, seem to be also deposited within the back-bulge Lagonegro depozone (Pescatore et al., 1988). Early Collisional Clastic Units (Late Burdigalian to Tortonian). Final closure of the Calabria-Lucanian (Liguride) remnant ocean basin and onset of continental collision in the southern Apennines are dated as early Miocene (Burdigalian). The provenance of the detrital components of the Miocene foreland sandstones, was dominantly from the Calabrian Arc terranes, the active growing front of the foldthrust belt (fig. 12). Nevertheless, folded and thrusted remnant oceanic sequences, active volcanics, and the forebulge of the flexed Adria margin were in time and space important detrital sources of the southern Apennines foreland basin system (fig. 12). The Source Areas of the Southern Apennines Foreland Basin System. The key sources of clastics deposited within the foreland basin system include different presentday realms (morphotectonic zones), that are: (a) The Basement rocks of the northern Calabrian Terranes. Initial signals of the provenance from northern Calabrian terranes is during final closure of the Liguride Complex (Saraceno Formation). During accretionary processes along the Adria margin, thrust units of the Calabrian terranes were in space and time accomodated (figs. 15, 16), producing an eastward displacement and related uplift. The thrust accomodation, uplift and unroofing history of the calabrian terranes is recorded within the southern Apennines foreland basin system (figs. 20, 22). (b) The uplifted subduction complex (the Calabro-Lucanian Flysch Unit). These oceanic terranes were uplifted during the mid-late Miocene representing an other important source of sediment (figs. 20, 23). (c) The Mesozoic to Tertiary Apulia/Adria basinal and platform domains (Lagonegro, Sannio, Sicilide units, the Alburno-Cervati-Pollino units, Verbicaro-San Donato- Bulgheria-Monti della Maddalena units, Monte Alpi unit, and the Apulia unit). The forebulge sources to the foredeep depozones, were the Alburno-Cervati-Pollino-Monti della Maddalena units from Burdigalian to Tortonian; the Monte Alpi unit, from early Messinian to lower Pliocene, and the Apulia unit, since Pliocene (fig. 21). (d ) Anadditional source of sediment is volcanic, that is mainly related to the calcalkaline volcanic arcs (Guerrera and Veneri, 1989), or more recently to the intraorogenic alkaline volcanism. Intracontinental rifting occurred in Sardinia during the Oligocene to Miocene. Subduction-related volcanism (between 32 and 11 Ma) was widespread along the western side of Sardinia (Cherchi and Montadert, 1982; Assorgia et al., 1986). This volcanism was subdivided in two main phases: calcalkaline eruptions of lavas, from 32 to 26 Ma, and explosive eruptions, which alternated or were contemporaneous with

37 the interplay of lithospheric flexure and thrust accomodation ::: 293 Fig. 22. Detrital evolution of the southern Apennines sandstones recording the unroofing history of the northern Calabrian terranes. Initial signals of the unroofing history occur during deposition of the Saraceno Formation; clastics were initially derived from sedimentary cover of the Longobucco Unit (A; Ls = sedimentary lithic fragments), and in the upper Saraceno Fm. from both sedimentary cover and the low-grade metamorphic basement rocks of the same unit (B; Lm = low-grade metamorphic lithic fragments). Thrusting of high-grade metamorphic rocks and deep erosion of the Calabrian terranes generated abundant gneissic (C; gneissic lithic fragment having garnet and sillimanite) and plutonic (D) detritus accumulated in the mid-late Miocene foreland basin system. A and B are from sandstones of the Saraceno Formation; C and D are from sandstone of the Cilento Group and Castelvetere Formation, respectively. effusive events, between 23 and 11 Ma (Beccaluva et al., 1985; Boni et al., 1990). The volcanic products of the first phase are andesite, basaltic andesite and basalt, whereas the second phase includes pyroclastic rocks of felsic composition (dacite to rhyolite). Burdigalian-early Langhian Foreland Basin System. Lower Miocene (Burdigalian) foreland basin clastics are widespread in the southern Apennines. Sediments of the upper Sicilide Complex represent the oldest deposits of the foredeep basin (Critelli et al., 1995b). In the forebulge and back-bulge depozones, a widespread quartz arenite, the Numidian sandstone, as well as shallow-water calcarenite and thin volcaniclastic layers were deposited (Selli, 1957, 1962; Perrone, 1987; Carbone et al., 1987; Carannante et al., 1988b; Santo and Sgrosso, 1988; Patacca et al., 1992; Sgrosso, 1998) (fig. 21). Siliciclastic strata of the Sicilide Complex (fig. 12) include quartzolithic, volcanolithic and quartzofeldspathic sandstones (fig. 11). Thick (up to 300 m) volcanolithic strata of the Tufiti di Tusa (fig. 24), include syneruptive (e.g. Critelli and Ingersoll, 1995) andesite and basaltic andesite sandstones (fig. 22), recording climax of volcanic activity of the calcalkaline volcanic arc (Critelli et al., 1990; Fornelli and Piccar-

38 294 s. critelli Fig. 23. Detrital signals of the uplifted Liguride subduction complex. Emersion of the Liguride Complex is signalled by the presence of abundant serpentinite (A; Sm = massive serpentinite), serpentine schist (B), glaucophanic schist (C; arrow indicates glaucophane), radiolarian chert (Ch), argillaceous chert and aragonitic limestones (CE) (D) lithic fragments. This ophiolitiferous detritus abruptly occurred during mid-late Miocene (Serravallian/Tortonian to early Messinian) foreland basin sedimentation. A and C are from sandstones of the Castelvetere Formation; B and D are from Piaggine Sandstone. reta, 1997). Interbedded with carbonatoclastic sequences of the Adria forebulge (the Capaccio-Roccadaspide, Cerchiara Formations; Carannante et al., 1988a), similar andesitic volcanolithic sand testifies to wide dispersal of the neovolcanic detritus in the forebulge and back-bulge depozones (Pieri and Rapisardi, 1973; Perrone, 1987; Pescatore et al., 1988; Critelli, 1991; Patacca et al., 1992). Metamorphiclastic quartzolithic and quartzofeldspathic sandstones occur in the lower portions of the Tufiti di Tusa below the volcaniclastic strata (Critelli et al., 1990), and characterize the Corleto, Colle Cappella and Albanella formations (fig. 20; Critelli et al., 1994; Fornelli and Piccarreta, 1997). They are derived from low to middle grade metasedimentary terranes, and are partly derived from ophiolitic rocks (Fornelli and Piccarreta, 1997). Interbedded thick carbonatoclastic (calcarenite-marl) strata within Tufiti di Tusa, Albanella and Corleto Formations, testify a provenance from the forebulge. Langhian to Tortonian Foreland Basin System. Since Langhian time, elongate turbidite basins have formed on top of advancing thrust-sheet systems (fig. 13). The Cilento Group, Serra Palazzo, Piaggine, Gorgoglione, Sorrento, Castelvetere, Oriolo, San Bartolomeo formations, Monte Sacro, Serra Manganile and Nocara Conglomerate formations (figs. 4, 6, 7) are the main turbiditic successions that were deposited after

39 the interplay of lithospheric flexure and thrust accomodation ::: 295 Fig. 24. Tufiti di Tusa Formation (Canale Coppozzolo section; southern Lucania). Thick volcaniclastic turbidite sandstone strata (a). Volcanic detritus (b) has andesitic composition and reflects provenance from early Miocene calcalkaline volcanic arc (Sardinia). the completion of rotation of Corsica and Sardinia (19±1 Ma; Dewey et al., 1989), in progressively shifting wedge-top and foredeep depozones of the growing foreland basin system. Except for the Serra Palazzo and Sorrento Sandstone, the base of each succession is everywhere marked by an unconformable contact (Patacca et al., 1990; Sgrosso, 1998). The Cilento Group (fig. 25) (Cilento Flysch according to Ietto et al., 1965), Langhian to Tortonian in age (Amore et al., 1988; Russo et al., 1995; Zuppetta and Mazzoli, 1997), ranging from 2000 to 1200 m thick, rests unconformably on the Liguride Complex, and in turn it is unconformably overlain by the upper Tortonian Gorgoglione Formation, and the upper Tortonian to lower Messinian (?) Monte Sacro, Oriolo and Serra Manganile formations (Critelli et al., 1995b). The Cilento Group consists of dif-

40 296 s. critelli Fig. 25. Schematic columnar section of the Cilento Group. It rests unconformably on Liguride Complex and it is unconformably covered by late Tortonian-early Messinian clastic wedges (Monte Sacro, Serra Manganile and Oriolo Formations).

41 the interplay of lithospheric flexure and thrust accomodation ::: 297 Fig. 26. Forebulge-derived gravity flows within the Cilento Group sequence. They are two impressive key-beds in the middle and upper Cilento Group sequence, that are 65m and 35m in thickness, respectively. ferent turbidite depositional systems (Valente, 1993). In addition to siliciclastic turbidite beds, the Cilento Group includes numerous carbonatoclastic megabeds (ranging from few meters to 65 m thick; fig. 26), olistostrome beds (ranging from tens to hundreds of meters thick), and coarse volcaniclastic debris flows and turbidites. Sandstones (fig. 20) of the Cilento Group are quartzolithic, volcanolithic and quartzofeldspathic (Critelli and Le Pera, 1994). Hybrid arenites and calcarenites characterize the carbonatoclastic

42 298 s. critelli megabeds. Sandstone strata of the lower portions are metamorphiclastic quartzolithic and quartzofeldspathic, resting on quartzolithic sandstone of the Liguride Complex. Proportions of volcanic and plutonic detritus increase upward in the upper Pollica Formation and lower San Mauro, Torrente Bruca and Albidona formations. A volcaniclastic interval in the lower San Mauro Formation includes abundant felsic (rhyodacite to rhyolite) calcalkaline volcanic clasts (Critelli and Le Pera, 1994). Sandstone of the upper Cilento Group is plutoniclastic quartzofeldspathic, consisting of abundant plutonic and metamorphic phaneritic fragments (fig. 22). In the upper Cilento Group thick carbonatoclastic and olistostroma megabeds record major tectonic events on both active thrust belt and forebulge (e.g. Critelli and Le Pera, 1994, 1998). Carbonatoclastic megabeds record huge volumes of sand-sized and mud derived from flexed Adria margin. These beds have impressive volumes and basinal lateral continuity (Colella and Zuffa, 1988; Cieszkowski et al., 1995). Olistostroma beds are siliciclastics, and include mountain-sized blocks of Calabrian terranes and Liguride Complex terranes (including also oceanic crust rocks; Ietto et al., 1965; Cocco and Pescatore, 1968; Carrara and Serva, 1982; Di Girolamo et al., 1992; Valente, 1991, 1993). Liguridederived detritus appear only in the middle-upper Cilento Group, suggesting initial signals of the Liguride Complex emersion. Clear signals of the Liguride Complex emersion and erosion are recorded within the Piaggine Sandstone (fig. 20; Serravallian to Tortonian; Sgrosso, 1981, 1998; Castellano et al., 1997). Quartzolithic sandstone of the Piaggine is derived from abundant Liguride Complex detritus (over than 50%; fig. 23), suggesting that near the Serravallian-Tortonian boundary, the Liguride Complex was in a subaerial position, probably representing the emerged frontal thrust of the mountain belt (Critelli and Le Pera, 1995a, 1998). The Serra Palazzo Formation (Selli, 1962; Ogniben, 1969) has been interpreted as the foredeep basin of the Langhian to Serravallian (Tortonian?) southern Apennines foreland region (Patacca et al., 1990). It has quartzofeldspathic sandstone (fig. 20), hybrid arenite, and calcarenite, suggesting provenance from both thrust belt and forebulge. The middle-upper part of the sedimentary succession, includes an olistostromal bed of carbonate clasts (olistoliths) (Loiacono and Sbarra, 1991) recording abrupt flexure along the passive margin. Sandstone of the Gorgoglione Formation (Selli, 1962), upper Tortonian in age (Patacca et al., 1990), is quartzofeldspathic having similar provenance to that of the upper Cilento Group sandstone. The Cilento and Gorgoglione sandstone modes record accretionary processes of the Calabrian terrane, and initial unroofing of the crystalline terranes (Critelli and Le Pera, 1994, 1995a, 1998). Late Collisional Clastic Units (Late Tortonian to Messinian). Southern Apennines Foreland Basin. The history of deep erosion of the Calabrian terranes is clearly recorded by upper Tortonian to Messinian clastics (fig. 14). These foreland clastics, including Castelvetere, Monte Sacro, Oriolo, Serra Manganile, Nocara, and San Bartolomeo formations (fig. 4), abruptly shift sand composition toward «ideal arkose» (e.g. Dickinson, 1985) or continental-block-derived sandstone (fig. 27),

43 the interplay of lithospheric flexure and thrust accomodation ::: 299 Fig. 27. QtFL plot (with superposed provenance fields of Dickinson, 1985) summarizing sandstone compositions from late Tortonian to early Messinian sedimentary assemblages deposited within the southern Apennines foreland basin system, and within the intermontane basins (northwestern Calabria) related to the backarc rifting of the Tyrrhenian Sea. Detrital modes of the Saraceno Formation, and Burdigalian to lower Tortonian foreland sandstones (only average values) are plotted as reference point of the unroofing history of the Calabrian terranes. Modified after Critelli and Le Pera (1998). suggesting deeply eroded Calabrian terranes. The previous forebulge of the Alburno- Cervati-Pollino-Monti della Maddalena units, during the late Tortonian was assembled within the fold-thrust-belt, and the new forebulge of the foreland basin system might be located on the Monte Alpi Unit (fig. 14; Patacca et al., 1992). Forebulge sedimentation of the Monte Alpi Unit (cf. Sgrosso, 1988b, 1998; Taddei and Siano, 1992) is thin (20 m to about 100 m in thickness) and consists of shallowwater to coastal arenite, marl and carbonate conglomerate (fig. 21). Arenite and rudite of the Monte Alpi are dominantly composed of carbonate detritus (fig. 28). Arenites of this forebulge sequence, are pure to impure calclithite, composed of ancient extrabasinal carbonate grains (e.g. Zuffa, 1987) having Cretaceous to early Miocene tests, and the siliciclastic detritus includes rounded to subrounded quartz, plagioclase, radiolarian chert, fine grained quartz-siltite and quartzite, and rare serpentinite/serpentine schist and volcanic lithic fragments. Rare quartzolithic sandstones, having abundant quartz, carbonate lithic grains and plagioclase, are interbedded with the calcilithite strata. Plutonic and metamorphic detritus are absent in these arenites. On the Alburno-Cervati-Pollino units, locally, thin arkosic sandstone strata unconformably overlain the Miocene forebulge sequence, or are directly on Cretaceous to Paleogene carbonates (cf. Patacca et al., 1992; Sgrosso, 1998). These arkosic strata crop out on the Alburno-Cervati Mountains (Tempa del Prato Sandstone) and on the Pollino Mountains (Civita Sandstone) (Patacca et al., 1992; Sgrosso, 1998; fig. 6), and

44 300 s. critelli Fig. 28. Late Miocene forebulge sediments of the Monte Alpi Unit. A) erosional surface (white line) between conglomerate strata (cgl.) overlying arenite strata (calclithite and calcarenite, ar). The conglomerate-arenite sequence unconformably covers the early-to-middle Miocene shallow-water strata or the Cretaceous limestone (Li) (here the cgl-ar sequence is in fault contact with Li); B) detail of the conglomerate sediments [A, B, Cima Santa Croce locality]. include abundant plutonic and high-grade metamorphic detritus, as such as extrabasinal carbonate detritus. Monte Sacro, Serra Manganile, Oriolo and Nocara Conglomerate formations (figs. 6, 7, 25), unconformably covering Liguride and Sicilide Complexes, and the Cilento Group, represent the wedge-top depozone sequences (figs. 14, 25).

45 the interplay of lithospheric flexure and thrust accomodation ::: 301 The Castelvetere Formation (Pescatore et al., 1970) has been interpreted as the foredeep basin sequence (Patacca et al., 1990; Critelli and Le Pera, 1995b; fig. 14). The Castelvetere has a thick olistostrome bed in the basal portions (fig. 29), including mountain-block carbonate olistholiths (Pescatore et al., 1970; Pescatore, 1978; Carrara and Serva, 1982), that record involvement of the Langhian to Tortonian passive margin (e.g., the Alburno-Cervati Unit) within the thrust belt. Castelvetere sandstone modes are plutoni-metamorphiclastic, with up-section increase of sedimentary detritus (Critelli and Le Pera, 1995b). Sedimentary detritus is carbonate-dominant in the lower Castelvetere; up-section increases of siliciclastic detritus suggests progressive erosion of older clastic wedges. Interbedded with quartzofeldspathic turbidite sandstone, the upper Castelvetere has a thick olistostrome bed composed of clastic detritus derived from Sicilide/Sannio and Liguride complexes, and a 1m thick volcaniclastic layer (fig. 29). The siliciclastic olistostroma may be the signal of the syn-thrust accomodation of the Sicilide/Sannio Complex and possibly of the Liguride Complex. The syneruptive volcaniclastic layer consists of pyroclastic fragments (pumice and shards) having felsic subalkaline composition (dacite) (Critelli and Le Pera, 1995b). Messinian sandstones of the wedge-top and foredeep basins (Patacca et al., 1990, 1992; Sgrosso, 1998), the Monte Sacro, Serra Manganile, Oriolo, Nocara, Tempa del Prato, Caiazzo, San Bartolomeo, Agnone formations have homogeneous quartzofeldspathic compositions similar to that of the Castevetere sandstone (fig. 27). Northeastern Calabria Foreland Basin. The Tortonian to Messinian strata of the northeastern Calabria represent the more proximal portions of the southern Apennines foreland basin system. These strata crop out along the piedmont of the Sila Massif, from the Trionto River (Rossano-Cariati zone) to south of the Neto River (Crotone zone) (fig. 6; cf. Cotecchia, 1963; Roda, 1964, 1967; Ogniben, 1973; Di Nocera et al., 1974; VanDijk, 1990; Van Dijk and Okkes, 1991; Roveri et al., 1992). The Crotone Basin is the most studied of these sequences, because of intense industrial explorations of dry gas (e.g. Roveri et al., 1992). The Tortonian to Messinian strata have been penetrated for more than 2000 m by AGIP in the Luna Field (shallow-water to onshore of Crotone zone; fig. 6). The Tortonian to Messinian stratigraphic sequence is unconformably over the Paleozoic plutonic and metamorphic rocks of the Sila Massif, or over the upper Oligocene to lower Miocene turbidite strata of the Paludi Formation (fig. 30; Roda, 1967; Roveri et al., 1992), and it represents the basin fill of a wedge-top depozone. The Oligo-Miocene sequence crops out extensively in the Trionto River Basin, whereas hypotetically may represent the basement of the Crotone Basin as shown in some seismic profiles (Roveri et al., 1992). Unconformably conglomerate and sandstone strata having rich macro-fauna (Clypeaster sandstone Formation, Cotecchia, 1963; or San Nicola dell Alto Formation, Ogniben, 1955; Roda, 1964) represent the onset of the foreland basin system on advancing Calabrian thrust belt. These strata include diverse sedimentary facies associations, representing a depositional sequence (Roveri et al., 1992), and they are interpreted as a turbiditic system, having an overall fining and thinning upward trend, in the Crotone

46 302 s. critelli Fig. 29. Schematic columnar section of the Castelvetere Formation. It rests unconformably on Mesozoic carbonate platform unit. Reconstructed stratigraphy is from personal data and from Pescatore et al. (1970), Cocco et al. (1974), and Sgrosso (1998). basin (where it is over 1000 m in thickness; Roveri et al., 1992). It represents the main reservoir of dry gas (Roveri et al., 1992). In the other areas, these strata include also continental strata (alluvial fans), nearshore and shallow-water deposits (area between Bocchigliero and Campana). These strata are overlain by fine-grained turbiditic systems and, toward the thrust culminations of the Sila Massif, by shelfal deposits. These strata, that are over 1000 m in thickness, correspond with the Ponda Formation (Roda, 1964) of the Crotone basin, or the «Argilloso-marnosa Formation» of the Rossano basin (Ogniben, 1955) and may represent deposition during low-stand systems tract (Roveri et al., 1992).

47 the interplay of lithospheric flexure and thrust accomodation ::: 303 Fig. 30. Schematic columnar sections of the Crotone and Rossano basins. The sedimentary successions rest unconformably on Paleozoic plutonic and metamorphic rocks of the northern Calabrian Arc (Sila Unit), or on Oligocene to lower Miocene Paludi Formation. These sequences represent the more proximal late Tortonian to Pliocene strata (wedge-top depozone) of the southern Apennines foreland basin system. Reconstructed stratigraphy is from personal data and from Ogniben (1962), Roda (1964, 1967), Romeo (1967), and Roveri et al. (1992).

48 304 s. critelli The Rossano wedge-top depozone, during late Tortonian-early Messinian, abruptly receives huge volumes of Sicilide-derived olistostroma «Argille Scagliose Formation» (Ogniben, 1955, 1962) composed by a variegated clay matrix and large blocks (olistholiths) of Cretaceous-Oligocene limestone, Miocene quartzolithic (similar to the Albanella-Colle Cappella sandstones) and quartzose sandstones (Numidian sands). These gravity flow deposits may be related to an out of sequence thrust accomodation or to a back-thrust of the Sicilide unit. Infact, at the same time interval, within the foredeep depozone, the Castelvetere Formation has a similar olistostrome layer (fig. 29; Critelli and Le Pera, 1995b). The Messinian sequence is characterized by evaporite deposits which record the Mediterranean salinity crisis. The evaporites consist mainly of gypsum and halite, followed by a thin mudstone interval, and thin clastic and evaporite beds (Ogniben, 1955; Roda, 1964; Romeo, 1967; Di Nocera et al., 1974). Overlying the evaporite sequence, an erosional unconformity marks the base of a late Messinian to Pliocene depositional sequence within the Crotone Basin (Roveri et al., 1992). This depositional sequence consists of a basal conglomerate and sandstone strata with finining-upward trend (transgressive systems tract; Carvane Conglomerate Formation; Roda, 1964), overlain by basin-wide marine shales (high-stand systems tract; Marne argillose dei Cavalieri Formation; Roda, 1964; Roveri et al., 1992). Northwestern Calabria Synrift Basin. Following the Tortonian tectonic phase (fig. 4), the foreland thrust-belt experienced intensive uplift, denudation and displacement toward the passive margin. The related foreland region experienced migrating foredeep and wedge-top depozones on the flexed passive margin; the Burdigalian to Lower Tortonian passive margin was involved in the thrust belt. The Tortonian tectonic phase terminated at c Ma, the time of youngest calcalkaline volcanism in Sardinia (Beccaluva et al., 1985), youngest metamorphism in the apenninic greenschist belt (Sartori, 1990), and youngest fission track signals of exhumed of both Hercynian and Alpine belt in Calabria (Thomson, 1994, 1998; fig. 16). Synchronously with major tectonic events in the foreland thrust-belt, extensional tectonic activity affected the whole Tyrrhenian Sea, just after the Tortonian compressive event; thereafter, evolution of the Tyrrhenian basin strongly influenced peripheral deformation of the Apennines foreland region (e.g. Malinverno and Ryan, 1986; Royden et al., 1987; Kastens et al., 1988; Lavecchia, 1988; Patacca et al., 1990; Sartori, 1990). Since late Tortonian, the Calabrian terranes have provided abundant detritus to both the foreland region and intermontane basins of the backarc region (figs. 4, 14). Clastic wedges on both sides are characterized by similar detrital provenances, and by fluvial, coastal and shallow marine, and minor basinal sedimentary facies (e.g. Roda, 1964; Ogniben, 1973; Di Nocera et al., 1974; Van Dijk, 1990; Van Dijk and Okkes, 1991; Colella, 1995). Sandstones of both marginal foreland and intermontane or synrift strata are «ideal arkose», and are identical in composition with the distal deep-marine upper Torto-

49 the interplay of lithospheric flexure and thrust accomodation ::: 305 nian to Messinian foreland strata (e.g. Critelli and Le Pera, 1995a; Critelli et al., 1995b) (fig. 27). Marginal syn-rift strata of the Coastal Range of western Calabria (Amantea Basin) has upper Tortonian to Messinian arkose, hybrid arenite and calcarenite. They do not seem to have direct correlations with sandstones of the Site 652 of the ODP Leg 107 (Borsetti et al., 1990), but all outcrops of the western Calabria were not investigated. Sandstone detrital modes of the Amantea Basin (peri-tyrrhenian area), however, are similar to sandstone strata of the Crotone Basin (peri-ionian area). Pliocene to Quaternary Clastic Units. Southern Apennines. During Pliocene, loading of the lithosphere by eastward thrusting of the Southern Apennines thrust-belt over the Adriatic plate resulted in flexural warping of the Apulia platform forming a downwarp, the Bradanic foredeep, an upwarp at the Apulia western edge, the Murge-Salento forebulge (figs. 8, 21). The Bradanic foredeep basin was initially filled by early Pliocene pelagic and turbiditic sediments, and from middle-upper Pliocene to Pleistocene by hemipelagic clays (Argille Subappennine; fig. 21), shallow-water calcarenite (Gravina Calcarenite Formation; fig. 19), deltaic, coastal and alluvial clastics (e.g. Casnedi et al., 1982; Casnedi, 1988; Pieri et al., 1996). Clastics of the bradanic foredeep depozones reflect the erosion of the previous accreted clastic and carbonate thrust units of the southern Apennines fold-thrust-belt. The Sant Arcangelo basin was one of the wedge-top depozone of the Pliocene-Pleistocene foreland basin system (e.g. Hippolyte et al., 1994a; b). Sediments of this basin show blended clasts from sedimentary thrust units, the uplifted subduction complex (Liguride Complex) and also from Calabrian arc. Most of the typical northern Calabrian provenances were trapped in piedmont areas of the Crotone and Rossano Basin, or within the Crati Basin. Because of the strike-slip movements were also active during Pliocene and Pleistocene in the southern Apennines realm, diverse fault controlled small basins were developed (e.g. Turco et al., 1990). Northern Calabria. The Sila Massif and the Coastal Range are the key physiographic and geologic elements of the northern sector of the Calabrian Arc. Both of these mountain ranges exhibit rates on the order of 0.8 to 1.1 mm/y (Sorriso-Valvo, 1993; Westaway, 1993). Estimated uplift rates are almost equal to late Quaternary denudation rates. Tectonics and climate have had a strong effect on the landforms of the Calabrian mountain ranges, resulting in the higher accumulation rates, on both Tyrrhenian and Ionian sides, than the entire Italian Peninsula (Barone et al., 1982; Sartori, 1982; Ibbeken and Schleyer, 1991; Knott and Turco, 1991; Chiocci, 1994; Trincardi et al., 1995). The Crati River represents the only moderately developed fluvial basin in the area, debouching into the Ionian Sea. The other alluvial-fluvial systems are mostly small coastal drainages. Additional Quaternary sediment sources for the Paola and Corigliano basins are active volcanic centres bordering the Paola Basin, and submarine structural highs, such as Amendolara embankment (Romagnoli and Gabbianelli, 1990), the latter

50 306 s. critelli bordering the Corigliano basin, and producing reworking intrabasinal detritus. Quaternary sedimentation of both basins is strongly influenced by glacio-eustatic sea-level changes (Chiocci, 1994; Trincardi et al., 1995). Crati Fan (northeastern Calabria). The Corigliano trough represents the Holocene submarine wedge-top depozone of the southern Apennines and northern Calabria foreland region (Pescatore and Senatore, 1986) (fig. 9). It is morphologically characterized by a restricted shelf area, numerous gullies and canyons, and a submarine fan, the Crati Fan, developed during Holocene and connected with the torrential-type Crati delta on the shelf (Ricci Lucchi et al., 1984; Romagnoli and Gabbianelli, 1990). The Ionian margin of northern Calabria consists of a moderately developed fluvial system, the Crati River and diverse smaller coastal drainages draining both Calabria continental block (i.e., Sila Massif) and the southern Apennines thrust belt (i.e., Pollino Massif) (fig. 9). The Crati River drains both the Calabrian crustal block to the west, east and south, and the southern Apennines Mesozoic to Tertiary sedimentary terranes to the north. The main-channel sand of the Crati River is quartzofeldspathic (Qm44 F38 Lt18; Qm54 K11 P35) with abundant metamorphic fragments (Lm96 Lv0 Ls4; Rg18 Rv0 Rm82) (Le Pera, 1998). The Pollino Massif is a dominantly siliciclastic and carbonate source area producing sedimentaclastic stream (Qm32 F23 Lt45; Lm5 Lv0 Ls95) and beach (Qm53 F13 Lt34; Lm22 Lv0 Ls78) quartzolithic sand. Detrital modes reflect a multicyclic provenance from siliciclastic and carbonate strata of the Pollino Unit, Liguride and Sicilide complexes, and the Cilento Group and younger sequences. The Sila Massif is a plutonic-metamorphic province, with subordinate sedimentary source rock, producing quartzofeldspathic stream (Qm33 F34 Lt33; Lm88 Lv0 Ls12) and beach (Qm47 F33 Lt20; Lm94 Lv0 Ls6) sand (fig. 31; Le Pera, 1998). Detrital modes reflect strong contribution from granodiorite and granite, gneiss and phyllite; sedimentary lithic fragments are also abundant and derive from Jurassic sedimentary successions (Longobucco Group). Crati Fan sand is quartzofeldspathic (Qm54 F24 Lt22) and metamorphiclastic (Lm78 Lv1 Ls21; Rg28 Rv2 Rm70). It is closely related to the sand composition of the Crati beach (Qm50 F26 Lt24) and main channel Crati River (Qm44 F38 Lt18) (Le Pera, 1998). Paola Basin (Western Calabria). The Paola Basin is a deep-marine, tectonically generated depression, that is the depositional site of the fluvial discharge of the Tyrrhenian margin of northern Calabria (e.g. Fabbri et al., 1981; Trincardi et al., 1995; Le Pera and Critelli, 1997; Le Pera, 1998). The Tyrrhenian margin of northern Calabria consists of diverse small coastal drainages, draining both Calabria continental block and the southern Apennines thrust belt, supplying sediments to the deep-marine Paola Basin. The basin is 70 km long, has maximum depth of 1000 m, and has Plio-Quaternary sedimentary fill that reaches a maximum thickness of about 5 km (e.g. Fabbri et al., 1981; Barone et al., 1982; Wezel, 1985; Argnani and Trincardi, 1993). The basement of the basin consists of crystalline rocks of the Calabrian terranes or the upper Tortonian to Messinian sedimentary sequences. The basal unconformity is early Pliocene in

51 the interplay of lithospheric flexure and thrust accomodation ::: 307 Fig. 31. QtFL plot (with superposed provenance fields of Dickinson, 1985) summarizing sand compositions for upper Pleistocene to modern sands of the Crati Fan, the Paola Basin (turbidite sands), and beach and fluvial sands of both Ionian and Tyrrhenian margins of northern Calabria. Sands from Ionian margin include the Crati Fan turbidites, the Crati River and Delta, the drainages derived from the Sila Massif and from the southern Apennines thrust belt. Sands from Tyrrhenian margin include Paola Basin turbidites, tephra layers interbedded with turbidites, coastal and fluvial systems of the Coastal Range. Data from Le Pera (1998). age, and sediments of this age are bathyal (Fabbri et al., 1981). The main Pliocene to early Pleistocene unconformities seem to be related to the abrupt uplift of the Calabrian Coastal Range (Catena Costiera; e.g. Ortolani, 1978; Fabbri et al., 1981; Barone et al., 1982; Wezel, 1985). Modern beach and fluvial sands of the Tyrrhenian margin of northern Calabria have three distinct petrofacies from north to the south, namely, (1) the calclithitic Lao petrofacies (at the northern end of the Paola Basin drainage area), having a provenance from the south-western flank of the southern Apennines slope, including dominantly Mesozoic carbonate rocks, (2) the quartzolithic Coastal Ranges petrofacies (in the central portion of the Paola Basin drainage area), having a provenance from dominantly metamorphic terranes (dominantly phyllite and schist, and gneiss) of the Coastal Ranges, and (3) the quartzofeldspathic Santa Eufemia Gulf petrofacies (at the southern end of the Paola Basin drainage area), having a provenance from metamorphic (dominantly gneiss, and phyllite and schist) and plutonic terranes of the Sila and Serre Mountains and from sedimentary terranes of the Catanzaro Graben. They represent the actualistic petrofacies of the mainland areas of the deep-marine Paola Basin (e.g. Le Pera and Critelli, 1997). Late Quaternary turbidite sands of the Paola Basin have distinct petrofacies (fig. 31), that are: (a) aquartzolithic petrofacies, including also calclithitic turbidite sands, and (b) avolcanic-rich petrofacies, including distinctive syneruptive volcaniclastic sands.

52 308 s. critelli The quartzolithic sand petrofacies widely occurs into the Paola Basin and it is strictly related to the composition of the Coastal Range littoral province. At the northern end of the Paola Basin, distinct sedimentaclastic (calclithitic) turbidite sands, reflects a provenance from the Lao littoral province (Le Pera and Critelli, 1997; Le Pera, 1998). The volcanic-rich sand petrofacies is also well represented within the Late Quaternary stratigraphic sequence of the Paola Basin. This petrofacies includes two main syneruptive volcaniclastic turbidites, one is located close to a datum plane at 20,000 y (calcalkaline volcanic provenance), and the upper one (alkaline volcanic provenance) is at the top of the basin-fill. Major paleotectonic events recordered by clastic sediments The Opening and Closure of Neotethys. Geodynamic history of the southern Italy terranes started during late Permian-early Triassic, after closure of the Paleotethys ocean. The Neotethys rifting started during Triassic, separing the Pelagonian and Pindos domains in the eastern Mediterranean. Clastic sediments related to this early Mesozoic plate reorganization in the Mediterranean region were confined in the Apulia region and in the nascent Lagonegro basin. Late Permian-early Triassic clastics of the basal Apulia platform, penetrated by exploration drillings at about 7000 m deep, may represent remants of red beds deposited during the earliest rifting stage of the nascent Neotethys or post-collisional clastics related to the Cimmerian orogen. The Early Triassic Monte Facito Formation (basal Lagonegro basin) is shallow-water quartzose sandstone and siltstone in the lower portions, and deep-water in the middle (Olistostrome interval) and upper (pelagic limestone and marl) portions (Marsella et al., 1991). Sandstone is quartz-rich, and the olistostrome interval includes also mafic volcanic clasts and blocks, that are basaltic in composition. The Monte Facito Formation may represent deposition following the Permo-Triassic lithospheric extensional phase and final break-up of Pangea. The presence of mafic blocks may be related to this Permo-Triassic transtension producing emplacement of mafic materials. During the Late Triassic and the Early to Middle Jurassic (fig. 10), Neotethys rifting produces abundant clastic sedimentation on the western margin, where Calabria was located. Continental redbeds, shallow-water to deep-marine quartzose sandstones are well developed as sedimentary cover of some basement units of the Calabria, Alpujarrides- Sebtides, Malaguides-Ghomarides, Kabylides, tectonostratigraphic terranes (e.g. Wildi, 1983; Bouillin et al., 1986). Quartzose turbidite sandstones were also present in the oceanic area (Liguride domain of southern Italy), and deposited from Jurassic to Paleogene (fig. 11). During the Paleogene and early Miocene, a drastic geodynamic change occur when the oceanic area located between the Adria margin and the Alboran block (Calabria microplate) was closed. Clastic sediments, filled the oceanic accretionary prism of the Liguride Complex, record the key geodynamic events of this oceanic closure (fig. 12). Sandstone compositions, ranging from quartzolithic and quartzofeldspathic to volcano-

53 the interplay of lithospheric flexure and thrust accomodation ::: 309 lithic, reflect provenances from the oceanic accretionary prism (abundant ophiolitiferous detritus) and from the active calcalkaline volcanism related to the subduction of the Adria oceanic lithosphere beneath the Iberian-European plates. The final closure of the Calabria-Lucanian remnant ocean basin is marked by initial unroofing of the thrustunits of the Calabrian terranes. This initial unroofing is clearly evident in the changing composition of the late Oligocene-early Miocene Saraceno Formation, where clastics show the progressive unroofing of the Sila Unit (fig. 12; e.g. Knott, 1987; Critelli and Le Pera, 1998). The Climax of Accretionary Processes and Evolution of the Foreland Basin System. The unroofing history of the Calabrian terranes, started during final closure of the Calabria-Lucanian oceanic basin, abruptly increased during accretionary processes over the Adria margin, occurred during early Miocene (fig. 12). The southern Apennines foreland basin system records the tectonic transport of the clastic detritus from the Calabrian thrust system. Increasing detrital feldspars and metamorphic detritus in the early Miocene sandstones (lower Cilento Group; upper Sicilide Complex) suggest dissection of the frontal thrust terranes of the northern Calabrian arc. Local huge arrivals of volcaniclastic detritus testifies the climax of activity of the calcalkaline volcanic arc of Sardinia (fig. 12). During middle Miocene (Serravallian to Tortonian) sandstone detrital modes recorded a major change from lower Cilento Group to upper Cilento Group and Gorgoglione Formation (fig. 19), with marked increased in detrital feldspars, medium- to high-grade metamorphic and plutonic rock fragments (Critelli and Le Pera, 1994). This compositional change, related to rapid northeastern movement of the Calabrian terranes and thrust accomodation of the high-grade Hercynian metamorphic rocks (fig. 16), reflects rapid rise of Calabria and sharp increase in denudation rates, as documented also by fission-tracks (e.g. Thomson, 1998). At this stage, the Adria (Alburno-Cervati-Pollino-Monti della Maddalena units) forebulge was involved in tectonic deformation and assembled within the orogenic belt (fig. 14); the Liguride subduction complex, that was part of the deep duplex system, locally emerges producing abundant detritus to the foreland (Piaggine Sandstone and Olistostroma beds of the upper Cilento Group; Critelli and Le Pera, 1995a, 1998) (figs. 20, 25). During upper Miocene (late Tortonian to Messinian), sandstone detrital modes recorded an other major change (increasing feldspars, high-grade metamorphic and plutonic fragments), and the composition shift toward «ideal arkose» (fig. 27; Critelli and Le Pera, 1995a). This time is also marked by the onset of the Tyrrhenian rifting on the back of the orogenic belt, causing an increased eastern displacement of the thrust system (e.g. Cello et al., 1981, 1989; Carbone and Lentini, 1990; Patacca et al., 1990; Lentini et al., 1994; Sgrosso, 1998). This other compositional change of the foreland sandstones reflects an increasing of the uplift rates, and deep erosion levels into mid-crustal rocks along the core of the Calabrian thrust belt.

54 310 s. critelli The Present Scenario. During Pliocene to Quaternary, the southern Apennines thrust belt is closely controlled by the flexural loading of the foreland lithosphere (e.g. Royden et al., 1987; Cinque et al., 1993; Doglioni et al., 1996). Since Pliocene, thrust propagation, normal block-faulting and sinistral strike-slip motion control the diverse morphotectonic zones of the southern Apennines and Calabria (Catalano et al., 1993; Cinque et al., 1993, Tortorici et al., 1995; Cello and Mazzoli, 1999). The flexural retreat of the foreland lithosphere may be the responsible for the differential thrust propagation and for arc generation, as well as for large block rotations in the upper plate. The lithospheric inhomogeneity and the detachment of the Adriatic lithospheric slab may also be responsible for the strong general Quaternary uplift of the axial and outer Apenninic belts (Cinque et al., 1993), as such as the Calabrian arc (Sorriso-Valvo, 1993; Westaway, 1993). The strong uplift of the northern Calabria arc since Pliocene, is responsible for the increasing denudation processes and the huge volumes of detritus. Most of these sediments are then transported by turbidity currents downslope and deposited within the Paola basin and the northern Ionian foreland basin (Critelli and Le Pera, 1998). The Crati fan, a 6000 years old turbidite system, may be considered a modern analogue of the Miocene turbidite systems filled the southern Apennines foreland basin. Its composition is quite similar to the Miocene sandstones (e.g. Critelli and Le Pera, 1994, 1998) suggesting close provenance relations and a similar paleogeographic scenario. Discontinuous Migration of Flexural features. The syntectonic Miocene stratigraphic succession indicates episodic, eastern migration of the forebulge. The position of the flexural forebulge did not progress continuously eastward through time but appeared to stall at its initial position from Langhian to Tortonian during deposition of the Cilento Group and Gorgoglione Formation (fig. 13). Only during the upper Tortonian to Messinian the forebulge moved rapidly eastward during deposition of Castelvetere and San Bartolomeo formations (fig. 14). Possible reasons for discontinuous migration of flexural features that may apply to the southern Apennines foreland are episodic migration of the thrust load and inhomogeneities within the lithosphere (e.g. Boyer and Elliot, 1982; Waschbusch and Royden, 1992; Giles and Dickinson, 1995). The flexural features do not migrate if the thrust load is not migrating. The buildup and migration of an accretionary prism includes progressive cratonward outstepping of the thrust front incorporates new material into the thrust load as it migrates (e.g. Giles and Dickinson, 1995). Thrust loads may also build up by almost vertical stacking of thrust sheets along ramps within the hinterland, producing the critical taper needed for the thrust system to migrate (e.g. Boyer and Elliot, 1982). In this case, flexural features would not continuously migrate cratonward because the thrust load itself is not continuously migrating cratonward. Waschbusch and Royden (1992) suggest that discontinuous migration of flexural features may also be caused by inhomogeneities within the lithosphere that fix the position of the forebulge to a weak segment of the foreland lithosphere.

55 the interplay of lithospheric flexure and thrust accomodation ::: 311 Flexed features of the southern Apennines foreland basin system change discontinuously during the last 23 my. The forebulge did not migrate from early Miocene to the Tortonian and it may have been fixed to a weak zone corresponding to the former miogeoclinal shelf margin of the Alburno-Cervati-Pollino inner platform domain (figs. 13, 21; Patacca et al., 1992). The Calabrian allochthon terranes and associated subduction zone progressively migrated toward the fixed forebulge until stresses reached a threshold during late Tortonian-early Messinian (fig. 14), the time of deposition of the Castelvetere Formation (Critelli and Le Pera, 1995b). At this time the forebulge migrated rapidly eastward causing deformation of the former back-bulge basin strata (Lagonegro basin). The inferred new forebulge may be the inner Apulia platform unit (or Monte Alpi Unit; figs. 14, 21). The Monte Alpi Unit has an unconformable lower Messinian carbonatoclastic sequence (figs. 21, 26), that is transitional to shallow-water (cf. Sgrosso, 1988a; b, 1998; Taddei and Siano, 1992), representing remnants of deposition on the forebulge. The last eastward forebulge migration occurs during Pliocene, and the new forebulge is the Apulia platform (fig. 21), and the foredeep is the Bradanic trough (fig. 8; e.g. Ricchetti, 1980; Ricchetti and Mongelli, 1980; Casnedi et al., 1982). Conclusions This study has examined clastic sediments and interpreted relative accomodation trends for many stratigraphic sequences that were deposited in the southern Apennines foreland basin system during the complex orogenic history of the western Mediterranean. Stratigraphic analysis of accomodation trends within syntectonic clastic units suggests that interplay of lithospheric flexure and thrust accomodation were important factors in controlling accomodation trends. Apart the earliest history of Triassic and Jurassic rifting phases, responsible of the oceanisation separing Apulia, Europe and Iberia plates, where clastic sediments are dominantly quartzose, the major clastic input is during final closure of the oceanic area (the Calabria-Lucanian remnant ocean basin) and the following accretionary processes along the Adria margin, occurred since Paleogene. Since Paleogene, the Calabrian terranes play a key tectonic role on the geodynamic processes affecting the southern Italy orogenic system. Since Oligocene, the Calabrian terrane drifted eastward from southern margin of the Iberia plate to collide and accreting over the Adria margin. Since closure of the remnant ocean basin, the northern Calabrian Arc has experienced accretionary processes, progressive exhumation and uplift of the tectonostratigraphic terranes, during growth of the southern Apennines foreland thrust-belt system. Changes in southern Apennines detrital modes in time and space, and creation of major unconformities marking different foreland sedimentary cycles, are responses of the morphogenesis and tectogenesis processes affected the northern Calabrian Arc. The Calabria-Lucanian remnant ocean basin was closed during early Miocene; clastic strata were deposited within an oceanic accretionary wedge, recording provenance from the active calcalkaline volcanism, accreted oceanic crust and from frontal tectonostratigraphic terranes of the northern Calabrian Arc (e.g., Sila Unit) (fig. 12).

56 312 s. critelli Earliest onset of continental accretion on Adria margin occurred during late Burdigalian-early Langhian; foreland clastic strata of the upper Sicilide Complex were derived from dominantly metasedimentary and related sedimentary cover rocks of the frontal Calabrian terranes. Sudden influx of neovolcanic detritus suggests continuing provenance from the active volcanic arc that was possibly hundred kilometers distant (fig. 12). Thick foreland clastic sequences formed during Langhian (fig. 13) over accreted Liguride and Sicilide Complexes. Langhian to Serravallian detrital modes of the Cilento Group (fig. 25) have abrupt changes from quartzolithic (phyllite and schist source rocks) sandstone to quartzofeldspathic (plutonic and gneissic source rocks) sandstone. This change in detrital modes was accompanied by interbedded carbonatoclastic detritus derived from abrupt flexure of the Alburno-Cervati-Pollino forebulge (figs. 25, 26). These major changes in foreland clastic deposition occurred c Ma (Critelli and Le Pera, 1994), the time of exhumation of the northern Calabria crystalline rocks (Thomson, 1994, 1998). Signals of sandstone detrital modes and fission tracks on source rocks indicate increasing uplift between 15 and 10 Ma, after which deep dissection affected the northern Calabrian Arc. During Serravallian to lower Tortonian (15 to about 10 Ma), abundant ophiolitic and pelagic detritus within the foreland basin (upper Cilento Group and Piaggine Sandstone) record emersion and erosion of the Liguride and Sicilide complexes. At c.11 Ma, volcanism of western Sardinia abruptly terminated, rendering Sardinia into a remnant arc. During late Tortonian to early Messinian, abrupt changes in the southern Apennines foreland region occurred. The former forebulge (e.g., Alburno-Cervati-Pollino units) was involved in tectonic deformation and incorporated within the thrust belt, and an eastward shifting of the foredeep depozone occurred. Foredeep and wedge-top sandstone strata shifted in composition toward continental block or arkose, suggesting major uplift of the Calabrian thrust belt. Coeval thrust accomodation of Sicilide-Sannio units, recorded as large gravitative deposits within foredeep and wedge-top depozones (figs. 29, 30) and recycling of older sedimentary sequences are important signals of accretionary processes within the thrust-belt. Signals of post-8 Ma volcanism are recorded in the foreland sequences, but sources are unknown. Since late Tortonian (10-8 Ma; fig. 14), backarc rifting has produced the Tyrrhenian Sea. At this time, the northern Calabrian Arc was the western border of the northern Ionian foreland region, and the eastern margin of the Tyrrhenian backarc basin (fig. 14). Intermontane and syn-rift basins of the western Calabria, and proximal and distal foreland basins of eastern Calabria and southern Apennines, have identical sand composition, plotting within ideal arkose or continental block provenance field (e.g. Dickinson, 1985, 1988) (fig. 27). The maximum rate of foreland thrust advancement (8 cm y 1 ) occurred in late Tortonian to Messinian (Patacca et al., 1990); major changes in uplift rate in the northern Calabrian Arc correspond with the abrupt change in sandstone detrital modes (Critelli and Le Pera, 1995a).

57 the interplay of lithospheric flexure and thrust accomodation ::: 313 Detritus derived from the elevated northern Calabrian Arc is still accumulating on the northern Ionian foreland and the Tyrrhenian backarc basin. Quaternary erosional rates for same areas of Calabria are over 200 mm/ka with maximum values exceeding 800 mm/ka (Ibbeken and Schleyer, 1991). The enormous sediment production of Calabria crosses the river-mouth areas and the beaches, and is spread over shelf and slope or is transferred via submarine canyons to lower bathyal plains of the Ionian and Tyrrhenian seas. Two of these basins, the Corigliano Basin, in the Ionian Sea, and the Paola Basin, in the Tyrrhenian Sea, record the sedimentary processes acting on the northen Calabrian Arc terranes and can be considered as a modern analogue of middleupper Miocene backarc/thrust-belt/foreland transect. The two margins of the northern Calabria record contrasting sand detrital modes in response of their different tectonic evolution (fig. 31). During Quaternary, in the southern Apennines thrust-belt, other major thrust accomodations, as such as normal faulting, sinistral strike-slip movement, block rotation and strong uplift occur defining the morphotectonic zones of the orogenic belt. The northern Ionian Sea and the Bradanic River basin represent the submarine and subaerial foredeep depozone, respectively. The Corigliano-Amendolara submarine basins, and the Sant Arcangelo basin represent the wedge-top depozones. The forebulge is finally located to the western Apulia platform, while the back-bulge depozone is located to the southern Adriatic Sea. The flexed foreland lithosphere and its forebulge has played an important rule to the development of the foreland basin system. The initially formed forebulge is interpreted to have been in the Alburno-Cervati-Pollino domain, and the final position of the forebulge is the present Apulia platform domain (figs. 8, 9, 21). Thus the forebulge migration distance was over 150 km. Forebulges contributed to the sediment supply within the foreland basin, even if it is minor with respect to the orogenic provenance. Forebulges have produced instantaneous huge volumes of single carbonatoclastic megabeds testifying major forebulge instability. In conclusion, the Calabrian microplate has played an important role in the dynamic evolution of southern Italy fossil and modern basins, representing the key tectonic element of the entire orogenic belt. It has been the most important source of detrital sediment supplied diverse basins. An estimation of detrital supply from Calabria, during the last 25 my, suggests that at least 5 to 8 km of crust has been removed from the Calabrian orogenic belt and deposited in the marine basins (Critelli and Le Pera, 1998). Erosional budgets and accumulation rates document the immense volume of detrital sediments transferred from deeply weathered crystalline rocks of the Calabrian Arc to marine basins. The clastic compositions of the southern Apennines foreland basin system reflect the changing nature of the thrust belt through time, recording the history of accretion of the Calabria microplate over the Adria margin. The type of sedimentary provenance analysis, providing an example of the close relations between clastic compositions and growing orogen in southern Italy orogenic system, may contribute and have general application to other major orogens.

58 314 s. critelli Acknowledgements I thank prof. F. C. Wezel for inviting me to write this paper, and for stimulating discussions on methodological conception of this work. I gratefully acknowledge discussions in the field, on foreland basin modeling and on Mediterranean geodynamics with J. Arribas, G. Bonardi, L. Brancaccio, A. Caggianelli, M. Castellano, G. Cello, A. Cinque, F. Chiocci, A. Colella, V. Cotecchia, B. D Argenio, P. de Capoa, P. G. De- Celles, G. Deiana, W. R. Dickinson, C. Doglioni, S. Fiore, E. Garzanti, P. Harabaglia, A. Iannace, A. Ietto, R. V. Ingersoll, E. Le Pera, F. Loiacono, A. Martin-Algarra, F. Matano, S. Mazzoli, C. Monaco, G. Mongelli, L. Morten, T. H. Nilsen, E. Patacca, V. Perrone, T. Pescatore, G. Piccarreta, P. Pieri, E. Piluso, G. Prosser, F. Ricci Lucchi, A. Rottura, P. Scandone, I. Sgrosso, M. Sorriso-Valvo, C. Tansi, F. Tateo, E. Tavarnelli, L. Tortorici, A. Tortosa, F. Trincardi, G. B. Vai, A. Valente, R. Valloni, F. C. Wezel, G. G. Zuffa, A. Zuppetta. An early version of the manuscript profited from critical reviews by F. C. Wezel, E. Le Pera, V. Perrone and M. Amelio. I am very grateful to profs. B. D Argenio, F. P. Sassi and F. C. Wezel for critical reviews of the final version of the manuscript. Work supported by funds of the Consiglio Nazionale delle Ricerche, grants to CNR-Istituto di Ricerca per la Protezione Idrogeologica nell Italia meridionale ed insulare (Grants to S. Critelli) and CNR-Istituto di Ricerca sulle Argille (Project: Sedimentary Basins Developed During Mesozoic- Cenozoic Tectonic Evolution of the Western Mediterranean, and Comparisons with Modern Sedimentary Basins; Resp. S. Critelli). References Acquafredda P., Lorenzoni S., Zanettin Lorenzoni E., The Bocchigliero Paleozoic sequence in the context of the Calabrian-Peloritan Hercynian Range (Italy). Geol. J., 29: Allen P. A., Homewood P., Williams G. D., Foreland basins: an introduction. In: P. A. Allen, P. Homewood (eds.), Foreland Basins. Int. Ass. Sediment., spec. pub., 8: Allen P. A., Crampton S. L., Sinclair H. D., The inception and early evolution of the North Alpine Foreland Basin, Switzerland. Basin Res., 4: Alvarez W., A former continuation of the Alps. Geol. Soc. Am. Bull., 87: Alvarez W., Cocozza T., Wezel F. C., Fragmentation of the Alpine orogenic belt by microplate dispersal. Nature, 248: Amato A., Ascione A., Cinque A., Lama A., Morfoevoluzione, sedimentazione e tettonica recente dell alta piana del Sele e delle sue valli tributarie (Campania). Geogr. Fis. Din. Quat., 14: Amodeo F., Molisso F., Kozur H., Marsella E., D Argenio B., Age of transitional beds from «Cherty Limestones»(Calcari con Selce) to «Radiolarites»(Scisti Silicei) in the Lagonegro Domain (Southern Italy). First evidence of Rheatian conodonts in Peninsular Italy. Boll. Serv. Geol. It., 110: Amodio Morelli L., Bonardi G., Colonna V., Dietrich D., Giunta G., Ippolito F., Liguori V., Lorenzoni S., Paglionico A., Perrone V., Piccarreta G., Russo M., Scandone P., Zanettin-Lorenzoni E., Zuppetta A., L arco calabro-peloritano nell orogene appenninico-maghrebide. Mem. Soc. Geol. It., 17: Amore F. O., Bonardi G., Ciampo G., De Capoa P., Perrone V., Sgrosso I., Relazioni tra Flysch interni e domini appenninici: reinterpretazione delle formazioni di Pollica, San Mauro e Albidona e l evoluzione infra-medio-miocenica delle zone esterne sudappenniniche. Mem. Soc. Geol. It., 41: Amore F. O., Basso C., Ciarcia S., Di Nocera S., Matano F., Torre M., Ciampo G., Di Donato V., Esposito P., Staiti D., Nuovi dati stratigrafici sul Pliocene affiorante tra il Fiume Ufita e il Torrente Cervaro (Irpinia, Appennino meridionale). Boll. Soc. Geol. It., 117: Argnani A., Trincardi F., Growth of a slope ridge and its control on sedimentation: Paola slope basin (eastern Tyrrhenian margin). In: L. E. Frostick, R. J. Steel (eds.), Tectonic Controls and Signatures in Sedimentary Successions. Int. Ass. Sediment., spec. pub., 20: Argnani A., Marani M., Savelli C., Galassi B., Migrazione del vulcanismo di arco cenozoico nel contesto geodinamico intraorogenico del Mar Tirreno meridionale: un riesame. In: R. Polino, R. Sacchi (eds.), Rapporti Alpi-Appennino. Accademia Nazionale delle Scienze, Roma:

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70 326 s. critelli Zuppetta A., Mazzoli S., Deformation history of a synorogenic sedimentary wedge, northern Cilento area, southern Apennines thrust and fold belt, Italy. Geol. Soc. Am. Bull., 109: Zuppetta A., Russo M., Turco E., Bartoli A., Nuovi dati sul «Flysch di Nocara»(Calabria settentrionale). Boll. Soc. Geol. It., 103: Pervenuta il 12 marzo 1999, in forma definitiva l 8 giugno Consiglio Nazionale delle Ricerche Istituto di Ricerca sulle Argille Via S. Loja-Area Industriale Tito Scalo PZ Consiglio Nazionale delle Ricerche Istituto di Ricerca per la Protezione Idrogeologica nell Italia meridionale ed insulare Via Cavour Roges di Rende CS [email protected]

71 the interplay of lithospheric flexure and thrust accomodation ::: 327 Relazione letta ed approvata nella seduta del 17 giugno 1999, sulla Memoria di Salvatore Critelli, presentata nella seduta del 12 marzo 1999 dal Corrisp. F. C. Wezel, intitolata: The interplay of lithospheric flexure and thrust accommodation in forming stratigraphic sequences in the southern Apennines foreland basin system, Italy. La Memoria di Salvatore Critelli consiste essenzialmente nell applicazione del modello del foreland basin system alla storia post-oligocenica della sovrapposizione della catena sudappenninica sulla microplacca adriatica. I bacini subsidenti di avanfossa sono sede di grandi accumuli di sedimenti clastici che provengono fondamentalmente dalle unità alloctone della catena orogenica dell Arco Calabro. All avanzare della catena, detti bacini migrano nello spazio e nel tempo. Stratigrafia, composizione e geometria delle successioni clastiche registrano le principali fasi tettoniche di avanzamento della catena a thrust verso l avampaese apulo e gli effetti del carico litostatico causato dalla messa in posto della catena sul margine passivo (forebulge). In tal modo le successioni clastiche dei bacini di foreland permettono di monitorare le fasi della messa in posto delle falde calabridi durante il Neogene-Quaternario, contribuendo a fissare precisi vincoli per ogni ricostruzione geodinamica e paleogeografica dell Appennino meridionale. Scopo del lavoro è dimostrare come la topografia prodotta dalla deformazione flessurale della litosfera adriatica abbia influenzato lo sviluppo della sedimentazione nei bacini del foreland sudappenninico, determinando, rispettivamente verso est, aree depresse profonde (bacini d avanfossa), aree lievemente rialzate ed aree lievemente depresse. A tal fine viene ricostruita, a partire dal Trias, la storia delle relazioni tra sedimenti clastici e i più importanti eventi geodinamici, registrata nelle principali unità tettono-stratigrafiche affioranti in Italia meridionale, fino ad arrivare alle attuali relazioni esistenti tra la catena sudappenninica e i bacini sedimentari del Mar Tirreno e dello Ionio. La Memoria rappresenta un interessante, moderno e lodevole tentativo di fare rientrare nella modellistica proposta dei bacini di avanfossa una grande mole di dati acquisiti dalla letteratura, che appaiono tuttavia essere selezionati in funzione della loro congruenza con la tesi sostenuta. Essa ha il merito di attirare l attenzione sull importanza della composizione dei sedimenti clastici per la ricostruzione dell evoluzione strutturale dei sistemi orogenici nello spazio e nel tempo. Da questo punto di vista, la ricerca di Critelli rientra nella grande tradizione nordamericana dei Pettijohn, Krynine e Dickinson. È anche possibile che il modello ricavato per l Appennino meridionale possa essere applicabile ad altri sistemi orogenici. In definitiva, il lavoro si segnala anche per il notevole sforzo operato dall Autore nell organizzare in forma «schematica», ma non sempre scorrevole e di facile comprensione, una ponderosa quantità didati geologici di grande complessità, sia spaziale che temporale. La Commissione, per i motivi esposti sopra e considerato anche il valore del suo contenuto culturale, propone all unanimità lapubblicazione integrale della Memoria. Francesco Paolo Sassi Forese Carlo Wezel Bruno D Argenio