Fracture stratigraphy of Mesozoic platform carbonates, Agri Valley, southern Italy

The outcropping platform carbonates form a layered succession crosscut by a dense array of bed-parallel pressure solution seams and veins, oblique-to-bedding pressure solution seams, and high-angle joints, veins, and pressure solution seams. Altogether, these structural elements form sub-seismic heterogeneities that formed during the polyphase tectonic evolution of the southern Apennines fold and-thrust belt, Italy. Aiming at assessing the role exerted by the primary carbonate architecture on failure modes and fracture geometry and distribution, we conduct a multi-disciplinary study by performing stratigraphic, petrographic, mineralogical, and mesoscale structural analyses. Based on carbonate rocks textures and fossil associations, three bed package associations associated to Pliensbachian-Toarcian, low-to-high energy open lagoonal, and Cenomanian, medium-to-high lagoonal-tidal depositional settings are assessed. Based upon specific failure modes, the aforementioned structural elements pertain to burial diagenesis, an early thrusting, a thrusting and a transtensional structural assemblages. Computed P20 (2D fracture density) and P21 (2D fracture intensity) values show that the primary interfaces present in the well bedded, low energy, open lagoonal carbonates compartmentalized fractures within single carbonate beds and bed packages. On the contrary, the aforementioned values show the absence of efficient mechanical interfaces in the medium-to-high energy lagoonal-tidal carbonates. This conclusion is confirmed by considering the P10 (1D fracture intensity) values computed for the most common diffuse fracture set. Moreover, the higher values are computed for the coarse grained lithologies, which is consistent with the control exerted by early chemical and physical compaction and cementation processes in the fracture stratigraphy of the study platform carbonates.