Fold-related deformation bands in a weakly buried sandstone reservoir analogue: a multi-disciplinary case study from the Numidian (Miocene) of Sicily (Italy)

Deformation bands, usually recognised in association with faults, are here analyzed in relation to a tight syncline fold developed in the Miocene Numidian turbidites of Sicily. Deposited above a growing thrust-wedge and then buckled during continued deformation, their porous sandstones form subsurface gas reservoirs elsewhere in the system and are analogues for deepwater systems in general. Structural data have been collected and statistically analyzed to characterise preferred orientations and size parameters (thickness, spacing, length) of deformation bands. Two distinct populations relate to folding: the most recent one is NE-SW oriented, which produced the most prominent structures, whereas an older one is partially obliterated. Microscopic investigation reveals porosity decreases within deformation bands with respect to host rock. The principal deformation mechanisms are grain rotation/sliding and pore-collapse, consistent with folding having occurred under low burial conditions. Within the thrust wedge, near-surface folding is widespread, as indicated by growth strata. Thus we expect early-burial deformation bands of the types (compaction an shear bands) illustrated here to be a component of reservoir damage in subsurface examples.