ABSTRACT Fold-thrust belts are commonly interpreted as ‘‘thin-skinned’’ structures, developed aboveadetachment, with the underlyingbasement remaining undeformed. However,inmany areas, particularly where compressional tectonism was preceded by rifting, models of basement fault reactivation may be more appropriate. The contrasts between thin-skinned and deep-rooting, inversion-dominated deformation in building fold-thrust complexes are investigated using a case history from the Italian Apennines. Three sectors were chosen to represent the marked lateral variations in structural style evident in the thrust belt. The outer portion of the Marche (in the north) is contrasted with a section through the Lucanian Apennines in the south and with the Molise district of the Central Apennines. The Marche structures are readily explained in terms of inversion, a model that is consistent with new deep seismic data onshore and conventional seismic from the nearby Adriatic Sea. The displacements implicit for the inversion model are a factor of five less than for existing thin-skinned interpretations. However, these styles are not applicable throughout the Apennines. Well data in the Southern Apennines of Lucania demonstrate large-scale thin-skinned thrusting, with 57 km of horizontal displacement since earliest Pliocene time. This includes 14 km of shortening that rampsupthrough the buried Apulian Platform carbonates. These deeper structures may be restored using ramp-dominated thrust geometries. The Molise sector shows broadly the same structural style as for Lucania: allochthonous shallow-water carbonates and pelagic basin units overlie the carbonates of the Apulian Platform, with the major difference being that here, the pelagic basin units are detached at the level of the Oligocene–lower Miocene Argille Varicolori. In this setting, the Apulian carbonates may be restored using only 5 km of displacement. The overlying allochthon probably has accommodated about 45 km of displacement since the earliest Pliocene. Therefore, the Apennines show differing structural styles with differing displacements along their length. Thick-skinned thrusting models may be applied to the Marche and to structures in the buried Apulian units.

Geological analysis of geophysical data obtained by the interpretation of crustal profiles indicates that in the central Mediterranean region the following structural domains can be distinguished: the foreland domains, an orogenic belt, and the Corsica-Sardinia block. The foreland domains are represented by two continental blocks, the Apulian block to the north and the Pelagian block to the south, belonging respectively to the Adria and to the Africa plates, separated by the oceanic crust of the Ionian Sea. The orogenic belt is located between two oceanic crusts: the old Ionian crust, at the present time subducting beneath the Calabrian arc, and the new crust of the Tyrrhenian Sea. The orogenic belt is represented by a multilayer allochthonous edifice composed of the Calabride chain, which tectonically overlies the so-called Apenninic-Maghrebian chain, which in turn is overthrust onto the upper Miocene and Pliocene top levels of a deep-seated thrust system that originated from the deformation of the innermost carbonates of the Apulian and Pelagian blocks (the external thrust system). The Calabride chain is composed of crystalline nappes originating, since the Eo-Oligocene, from the delaminated margin of the Europe plate. The Apenninic-Maghrebian chain tectonic units derive from the orogenic transport during Oligo-Miocene times of sedimentary sequences deposited in paleogeographic domains located between the Europe and the Afro-Adria plates. These units are composed of meso-Cenozoic shallow-water carbonate successions detached from a continental type of crustal sector named here the Panormide-Apenninic block. This is now recognizable by means of seismic lines shot in the Tyrrhenian off-shore of the southern Apennines and northern Sicily. The meso-Cenozoic basinal units that constitute the Apenninic-Maghrebian chain can be distinguished into two main groups of sequences, originally located on oceanic crusts separated by the Panormide-Apenninic crust: the external ones (Ionides) related to an original basin belonging to part of the Ionian paleo-basin involved in the orogenesis (Lagonegro, Imerese, Sicanian, and Monte Judica units) and the internal ones ascribed to the Alpine Tethys (Liguride-Sicilide units). The previously described allochthonous edifice is characterized by thin-skinned tectonics and represents a roof thrust system resting on the external thrust system, which derived from thick-skinned tectonics that produced folds and reverse faults with relatively moderate horizontal displacements. The external thrust system developed from late Miocene times, contemporaneously with the opening of the Tyrrhenian basin, and is named the Apulian thrust system in southern Italy and the Pelagian-Sicilian thrust belt in Sicily. The crustal sections of the CROP project (Deep Seismic Exploration in the Central Mediterranean and Italy) allow us to distinguish the thickness and distribution of the crusts in this area of the Mediterranean Sea, and they confirm that the foreland continental blocks, the Apulian and the Pelagian blocks, are separated by the Ionian oceanic crust. Both the foreland blocks extend below the orogenic belt, reaching the Tyrrhenian margins, with a gradual thinning and a transition to a Paleo-Ionian slab, probably not active at present time, from which the Ionides detached and overrode the external thrust system. The seismogeological data indicate the presence of a continental block, original basement of the Panormide-Apenninic platforms, that took part in the closure of the sectors of the Paleo-Ionian Sea interposed between the Panormide-Apenninic crust and the Pelagian and Apulian blocks. At the present time, it is colliding with the foreland blocks. Thus, this has been identified as collisional crust. The geologic evidence of this collisional stage is manifested in the northwest-southeast-oriented South Tyrrhenian system, which is characterized by dextral faults affecting both off-shore and on-shore areas of Sicily. A mirrorlike sinistral fault system occurs in the southern Apennines. Interpretative seismic reprocessing has permitted clear seismic imaging of the subducted Ionian slab. The distribution of the earthquakes transversally and longitudinally indicates that the slab is narrowing in a vertical direction; thus, at present, the active slab is limited to a short segment between northeastern Sicily (the Vulcano line) and southern Calabria (the Catanzaro line). To the west and to the northeast of these lines, a collisional setting can be recognized. The geological and geophysical data and the volcanological characteristics of the study area permit us to restore the paleogeographic and paleotectonic setting and have allowed us to recognize three orogenic stages: the Eo-Alpine, which originated during Cretaceous–Eocene times but is less evident in the study area; the Balearic stage (late Oligocene–early Miocene), in which the Corsica-Sardinia block collided with the Adria-Africa margins with thrusting of the Alpine Tethydes over Panormide units; and the Tyrrhenian stage (middle Miocene to present), when the onset of the Tyrrhenian back-arc basin occurred and the collisional crust followed the Ionian slab retreat, closing the interposed basin with tectonic transport of the Ionian ocean cover (the Ionides) over the foreland blocks.

Abstract Hydrocarbon distribution in the Southern Apennines thrust belt of Italy is directly related to the geological characteristics and complex evolution of the thrust tectonic pile involving units from different palaeogeographical domains. Within this structural–stratigraphic context, the main exploration target is represented by the carbonate units of the Apulian Platform, which contain the largest and deepest oilfields in the region. By integrating different types (e.g. wells, seismic, maps, reports) of legacy public and confidential data of various vintages, the subsurface structural setting of the contractional Apulian structures around the Benevento Field in the Southern Apennines hydrocarbon province is reconstructed. The discovery dates back to the early 1970s. The reservoir consists of Cretaceous–Lower Miocene carbonates at a depth of around 3000 m below sea level bearing both oil and gas. A new digital interpretation and integration, which takes into account the most recent understanding of the evolution of this thrust belt, has allowed reconstruction of the trap style of the Benevento Field and of the prospective (undrilled) structures in the surrounding area. A history of positive inversion tectonics is interpreted from a 2D kinematic restoration; this has important implications for both the structural style and the hydrocarbon prospectivity of the Southern Apennines thrust belt.

ABSTRACT The Campano-Lucano Arch is a major hydrocarbon province in the Southern Apennines of Italy. To provide new understanding of the thrust-belt architecture while constraining the derived interpretation of buried structure, we have analyzed data from seismic-reflection, wells, surface geology, 3-D computerized reconstructions, and sandbox simulations and integrated these data into a regional-scale structural model. Results show that refolding of already folded and thrusted units models the current structural setting, in which shallow and deep structures interact to form the recognized tectonic framework. In the region, recent folding and thrusting of the deeper autochthonous substratum reworked an early-phase vertical allochthonous assemblage, which ultimately behaved like a new pseudo-multilayered stratigraphy. Three-dimensional strain partitioning is moderately homogeneous across the thrust belt’s internal domain, because shallow and deep structures show minor mechanical disharmony. Conversely, distribution of the deformation is strongly inhomogeneous across the thrust belt’s external and marginal domains, both vertically and horizontally (along strike). Interference, through time and space, between the related noncylindrical, shallow (the “Apenninic” Thrust Belt) and deep (the “Apulian” Thrust Belt) contractional systems has developed a “dome and basin” structural pattern that characterizes the current tectonic architecture and that may localize, at depth, the main oil accumulations in the region.