Fold-related deformation bands: an analogue of a shallow-burial reservoir from Numidian turbidites of Sicily

Deformation bands are widely recognized in association with faults (Fossen et al., 2007), but here we examine their relationship to folding. Such structures, together with joints and faults, are generally reported from a variety of stress-field settings (shear, compression, extension). Here, we report deformation bands related to a tight syncline developed in the Miocene Numidian turbidites of Sicily. These porous sandstones, deposited above a growing thrust wedge and then buckled during continued deformation, form subsurface gas reservoirs and are analogues for deepwater systems. Structural data indicate two distinct populations related to folding: the most prominent and recent structures are NE-SW oriented, whereas an older one is partially obliterated. Multi-disciplinary analyses (petrography, petrophysics, X-ray-microtomography) show a general decrease of porosity in deformation bands with respect to host rock, even though a few shear structures reveal an increase of porosity. The principal deformation mechanisms are grain rotation/sliding (Fossen et al., 2007) and pore-collapse (Aydin et al., 2006), consistent with folding having occurred under low burial conditions. Therefore, our study reveals deformation bands can increase the complexity petrophysical properties of subsurface sandstone reservoirs - not only around fault zones but also across fold structures.