Research paperStructural properties of fractured and faulted Cretaceous platform carbonates, Murge Plateau (southern Italy)

- We studied background and fault-related deformation in tight carbonates.
- Background deformation consists of bed-parallel stylolites and two sets of cross-orthogonal bed-perpendicular joints.
- We differentiated syn-sedimentary Cretaceous from post-Cretaceous faults.
- The permeability of the fault zones is strongly dependent on their architecture and mechanisms of the faults growth.
- Fluid storage and migration pathways are also controlled by dissolution/cementation processes in the fault zones.

The Upper Cretaceous carbonates cropping out in the Murge Plateau are good analogues of the fractured and faulted carbonate oil reservoirs of southern Italy. For this reason, a detailed field analysis focused on structural architecture of fault and fracture networks has been carried out in the Murge Plateau. The well-bedded carbonates exposed there are crosscut by a set of bed-parallel stylolites and two sets of bed-perpendicular cross-orthogonal joints/veins. These structural elements were likely formed under vertical loading during burial diagenesis and flexure of the Apulian foreland of the Southern Apennines fold-and-thrust belt. Bed-parallel stylolites and bed-perpendicular cross-orthogonal joints/veins represent the background deformation that was overprinted by the fault-related localized deformation. The fault sets documented in the study area are arranged in two kinematically-compatible fault networks. The first one is made up of WNW-ESE and NNW-SSE oriented strike-slip faults, right- and left-lateral, respectively, and NW-SE oriented normal faults. The second fault network consists of WNW-ESE oriented left-lateral strike-slip faults, and NE-SW oriented normal faults.First, both architecture and dimensional parameters of the fault and fracture networks have been characterized and computed by means of statistical analysis. Then, the permeability structures associated to the aforementioned networks have been assessed in order to determine the role exerted by fault architecture and dissolution/cementation processes on the fluid storage and migration pathways within the studied platform carbonates. Network 1 faults show a quite variable fluid behavior, in which the fluid flow is strongly affected by inherited structural elements and karst dissolution, whereas network 2 faults show a more uniform, fluid conduit behavior.