Structural setting along the CROP-04 deep seismic profile (Southern Apennines - Italy)

An updated review of the Southern Apennines structural architecture, a proven petroleum province in Italy, is presented taking into consideration the new stratigraphic and structural constraints provided both by almost forty years of petroleum exploration and by the recently reprocessed CROP-04 deep seismic reflection profile. A regional geological cross-section, drawn nearly parallel to the CROP- 04 seismic line, is described and discussed to point out the main features of the Southern Apennines. Moreover, a second shorter crosssection (named M. Foi cross-section), very well constrained by good quality seismic and well data, is used to describe the allochthonous units structural setting in detail, with special attention to the tectonic evolution of the Lagonegro units. The Southern Apennines (SA) are a Neogene and Quaternary thrust belt located in the hanging wall of a W-directed, E-retreating, subduction of the Apulo-Adriatic lithosphere. From a structural point of view, the SA are made up of a huge duplex system consisting of two main units: the allochthonous nappes and the Apulian platform. The allochthonous units, derived from the deformation of both peritidal carbonate platforms and pelagic basin successions and from the stratigraphically overlying foredeep deposits, are completely detached from their original substratum and transported onto the carbonates of the Apulian platform. Beneath the mountain chain the Apulian carbonates are deformed to form a buried antiformal stack. Some outstanding problems concern both the structural setting of the deeper part of the SA thrust belt (e.g. the degree of involvement of the crystalline basement in the Apulian antiformal stack) and of the allochthonous nappes. CROP-04 and well data suggest the possibility that Lagonegro and Apulian Platform carbonate units could extend at depth westward below the Apenninic platform units. Moreover, some geological and geophysical evidences suggest that shortening within the Apulian carbonate platform units might be significantly greater than previously assumed in several recent structural interpretations. The increased shortening hypothesis may have relevant implications for a better understanding of the petroleum system evolution. The complex antiformal stack-type structure of the Lagonegro units, revealed by well data and characterised by the tectonic repetition of the couple «Scisti Silicei» plus «Calcari con Selce», could be reproduced with a relatively simple series of ramp-flat thrusts propagating through the Lagonegro succession. Based on both the regional and the M. Foi cross-sections, a likely original width of about 125 km has been estimated for the Lagonegro basinal domain: 90 km are now deformed in antiformal-stack type structures in the axial zone of the Campania-Lucania arc while other 35 km might be buried, in our interpretation, below the Apennine units. The resulting total internal shortening for the Lagonegro domain is about 60%.