Nucleation, development and petrophysical properties of faults in carbonate grainstones: evidence from the San Vito Lo Capo peninsula (Sicily, Italy)

Detailed field mapping and microstructural and textural analyses carried out in Lower Pleistocene grainstones in the San Vito Lo Capo peninsula (in north-western Sicily) revealed document failure modes and fault development in porous carbonate grainstones. Individual com-pactive shear bands represent the simplest fundamental shear structures, while pressure solution processes commonly localize within previously developed compactive shear bands. In the Lower-Pleistocene carbonate grainstones of San Vito Lo Capo peninsula, composed of eroded car-bonate and marl fragments, pressure solution processes localize mostly grain-to-grain, leading to the formation of zones of weakness which facilitate slip and significant displacement. The transition from one deformation process to another is likely controlled by changing material properties and anisotropy within the bands. Finally, laboratory analyses of representative fault rock samples show that the structures described above have sealing capacity with respect to the host rock, and may compartmentalize any geofluid reservoir.