No abstract

In the southern Apennines fold-and-thrust belt, thermal indicators record exhumation of sedimentary units from depths locally in excess of 5 km. The thrust belt is made of allochthonous sedimentary units that overlie a 6-8-km-thick, carbonate footwall succession. The latter, continuous with the foreland Apulian Platform, is deformed by reverse faults involving the underlying basement. Therefore, a switch from thin-skinned to thick-skinned thrusting occurred as the Apulian Platform carbonates-and the underlying thick continental lithosphere-were deformed during the latest shortening stages. Apatite fi ssion track data, showing cooling ages ranging between 9.2 ± 1.0 and 1.5 ± 0.8 Ma, indicate that exhumation marks these late tectonic stages, probably initiating with the buttressing of the allochthonous wedge against the western margin of the Apulian Platform. Pliocene-Pleistocene foreland advancing of the allochthonous units exceeds the total amount of slip that, based on cross-section balancing and restoration, could be transferred to the base of the allochthon from the underlying thick-skinned structures. This suggests that emplacement of the allochthon above the western portion of the Apulian Platform carbonates was followed by gravitational readjustments within the allochthonous wedge, coeval-and partly associated with-thick-skinned shortening at depth. The related denudation processes are interpreted to have played a primary role in tectonic exhumation.

Thrust propagation through previously rifted continental margins may result in fold and thrust belts whose structure is strongly controlled by the inherited basin architecture, as it occurs in southern Italy. The Lagonegro units of the southern Apennines comprise a deformed pelagic basin succession showing variable stratigraphic characteristics, mainly lateral variations in both facies and thickness, interpreted to be due to a complex basin topography related to a Triassic rifting event. In contrast to previous studies, cross-section balancing and restoration indicate that the Lagonegro units exposed in the high Agri Valley area suffered relatively limited internal shortening (8 km, i.e. 35%). Early deformation of these rocks, later incorporated into a large-displacement thrust sheet, was dominated by folding around (present-day) roughly north–south-trending axes. The attainment of a regional décollement level was favoured by an early mild inversion of the basin, producing a roughly similar structural elevation of both hanging-wall and footwall successions to Mesozoic faults. Most of the contractional deformation was accommodated by buckling of the Mesozoic syn-rift strata between synsedimentary faults, which represented major mechanical interfaces. Early strain localization in the Lagonegro Basin ahead of the active thrust front was most probably mechanically controlled by a faulted crustal segment which originally lay, within the continental margin, between two massive carbonate platforms.

Detailed geological mapping and new stratigraphic and structural data collected in the Lucania area of the southern Apennines allowed us to assess the deformation history of Il Monte-Corleto Perticara zone, in the High Agri Valley (Lucanian Apennines, southern Italy) where red and green shales (known as Argille Varicolori or Argille scagliose) crop out. Our observations suggest that: (1) ‘chaotic’ facies within the Argille Varicolori may be attributed to a broken formation generated by overthrusting of Apenninic Platform units onto already deformed Lagonegro basin strata; (2) gravity sliding phenomena at the thrust front enhanced the development of debris flow and the emplacement of olistostromes at distances of up to tens of kilometres from the leading edge of the Apenninic Platform thrust; (3) the above processes probably ended in mid-Miocene time, as suggested by observed structural and stratigraphic relationships among accreted terranes and synorogenic deposits. The evolutionary model envisaged here could also be relevant in other active convergent zones, where seismic and drilling data are sparse, and in subaerial fossil margins where broken formations occur.

This case study was undertaken for a low-porosity fractured carbonate reservoir with a complex fracture network resulting from several phases of tectonic activity. The integration of the image log and seismic-derived interpretations was problematic due to the complexity of the image log signature and the variable quality of the surface seismic data. Earlier experience indicated that VSPs may provide information on faulting and/or fracturing that may otherwise be difficult to determine with confidence from other data sources. Consequently, specialist VSP processing techniques were used to identify and map reflectors in three-dimensional space. Data acquired in two wells were reprocessed to interpret structural features and determine their geometries. The interpreted VSP reflectors were validated and integrated with the analyses of image logs and the interpretation of surface seismic data providing a constrained structural model that allowed the interpretation of seismic data away from well control and provided a starting point for seismic interpretation in areas where structural geometries were poorly imaged on surface seismic. It is shown that VSP, including vertical incidence, data can contribute to the understanding of reservoirs and enables well-derived information to be extrapolated away from the wells.