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

Abstract

AbstractThe Viggiano Mt. platform carbonates form a layered succession cross-cut by a dense array of pressure solution seams, and five sets of fractures and veins, which together form a sub-seismic structural network associated with polyphasic tectonic evolution. To assess the influence exerted by depositional and diagenetic heterogeneities on fracture geometry, distribution and multiscale properties, we present the results of stratigraphic, petrographic, mineralogical and mesoscale structural analyses conducted at the Viggiano Mountain, southern Italy. Based on rock textures and fossil associations, we documented that the Sinemurian–Pleinsbachian carbonates were deposited in a low-energy open lagoon, the Toarcian carbonates in a ramp setting rimmed by sand shoals, and the Cenomanian carbonates in a medium- to high-energy, lagoonal–tidal setting. Fracture-density (P20) and intensity (P21) values computed after circular scanline measurements show similar trends in both Sinemurian–Pleinsbachian and Toarcian carbonates, consistent with the bed and bed-package heterogeneities acting as efficient mechanical interfaces during incipient faulting. On the other hand, P20 and P21 do not show very similar variations throughout the Cenomanian carbonates due to pronounced bed amalgamation. Throughout the study area, the aforementioned parameters do not vary in proportion to the bed thickness, and show higher values within the coarse-grained carbonate beds. This conclusion is confirmed by results of linear scanline measurements, which focus on the P10 properties of the most common diffuse fracture set. The original results reported in this work are consistent with burial-related, physical–chemical compaction and cementation processes affecting the fracture stratigraphy of the Mesozoic platform carbonates.