Deformation bands in Numidian sandstones of Sicily: a petrographic-structural study

Here we consider the Numidian turbidite system (Miocene) of Sicily as analogue for a variety of deepwater hydrocarbons reservoirs. In particular, we carried out a detailed petrographic-structural investigation on sandstones cropping out near the village of Sperlinga (central Sicily - Italy). The main outcrop consists of a roughly NW-SE trending km-scale wavelength syncline fold, transversally sliced by left-lateral strike-slip faults NE-SW oriented, associated with a younger regional-scale right-lateral shear zone according to Carbone et al. (1990). Our study shows that an intricate network of different generations of deformation bands (DBs) widely occur in the area. Petrographic observations highlight different typologies of DBs: cataclastic- shear- dilation, and compaction-type bands, suggesting a shear component mixed to a contractional one. The classic rock assemblage is given essentially by quartz (often consisting of polycrystalline clasts showing blocky extinction and preferred shape orientation), with minor amount of plagioclase, K-feldspar, chlorite, mica, zircon, glauconite. The structural analysis and trends indicate that DBs are possibly associated with a previous low-angle thrust contact developed during the early stage of tectonic piling. Currently, the thrust damaged zone is well exposed indoors the castle of Sperlinga, where it appears strongly tilted up to exhibit subvertical boundaries trending NW-SE. The great circles of poles of DBs planes are oriented NW-SE and NE-SW sub-perpendicular and/or oblique (at about 30 degrees) to the current maximum compressional stress direction, roughly N-S oriented. Considering that Numidian outcrops in Sicily have experienced a c. 100 CW rotation since deposition (Speranza et al., 2003; Pinter et al., 2016a) we restored the succession by operating first a tilt correction (of ca. 60 degrees of the originally low-dipping angle thrust surface) and then a second rotation (back of about 100 degrees CCW) around a vertical axis. The data indicate that the turbiditic channel system, N-S oriented at the time of sedimentation (Pinter et al., 2016b), deformed under an E-W trending shortening axis consistent with Neogene thrusting in the central Mediterranean. Further investigation should reinforce our preliminary results. References Carbone S., Catalano S., Grasso M., Lentini F., Monaco C., 1990. Carta geologica della Sicilia centro-orientale. S.El.Ca, Firenze. Pinter, P.R., Butler, R.W.H., Hartley, A. J., Maniscalco, R., Baldassini, N., Di Stefano, A., 2016a. The Numidian of Sicily revisited: A thrust-influenced confined turbidite system. Mar. Pet. Geol., 78: 291–311. doi:10.1016/j.marpetgeo.2016.09.014 Pinter, P.R., Butler, R.W.H., Hartley, A.J., Maniscalco, R., 2016b. Deep-water sandstones in tectonically complex systems: the Numidian of Sicily as an example. 88° Congresso SGI, Napoli 2016. Rend. Online Soc. Geol. It., Suppl. n. 1 al Vol. 40 (2016): 501. Speranza, F., Maniscalco, R., Grasso, M. 2003. Pattern of orogenic rotations in central-eastern Sicily: implications for the timing of spreading in the Tyrrhenian Sea. Journal of the Geological Society, 160, 183-195.