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

Abstract

The 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.

Depositional Setting, Diagenetic Processes, and Pressure Solution-Assisted Compaction of Mesozoic Platform Carbonates, Southern Apennines, Italy

“…The latter carbonates contain bivalve shells (Lithiotis), foraminifera (Siphovalvulina sp., Pseudocyclammina liassica), and green algae (Palaeodasycladus mediterraneus). The low-energy carbonates are topped by oolitic grainstones, which were originally deposited on a carbonate ramp rimmed by sand shoals [30,46].…”

“…consists of Cretaceous limestones made up of carbonate grainstones, rudstones, floatstone with rudist fragments, and sporadic mudstones. These rocks were originally deposited during Albian-Cenomanian in a high-energy shelf environment close to the platform margin [30,46]. At Viggiano Mt., the present work focuses on the carbonated exposed at two sites labeled as Scarrone la Macchia (SLM) and Il Monte (ILM), respectively (Figure 1).…”

“…The exposed carbonates at the SLM site are sub-divided into two informal units [30] (Figure 2a,c). Starting from the base, the well-layered unit consists of about 13 m thick shallow-water limestone.…”

“…The carbonate described at the SLM site was originally deposited in an inner-platform depositional environment, which was characterized by presence of a carbonate sandy margin protecting the lagoon [30]. Furthermore, the association of benthic foraminifera (including Haurania sp., Siphovalvulina sp., Lituosepta sp.)…”

“…The studied Mesozoic shallow-water carbonates were recently analyzed in terms of their fracture stratigraphy properties [30], modalities of pressure solution processes associated with sedimentary burial-and thrusting-related stress conditions [19], multiscale fault and fracture geometry and distribution [31], and multiscale fracture porosity and permeability characteristics. Focusing on the diagenetic processes during the sedimentary burial (sensu [19]), we first decipher the relative timing of precipitation of the calcite cements in the various carbonate lithofacies, we assess the diagenetic environments in which they formed, and then we document the crosscutting relationships between bedparallel stylolites and cements.…”