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54 E. Tondi et al. / Journal of Structural Geology 37 (2012) 53e64
already compacted bands, pressure solution is the main process 2. Geological framework
responsible for grain-size reduction (Tondi, 2007), which could be
also defined dissolution/cementation bands sensu Fossen et al. Favignana is the largest of the Egadi Islands, and is located in
(2007). Eventually, further deformation facilitates slip along pre- NW Sicily along the southern edge of the Tyrrhenian Sea (Fig. 1a).
existing stylolites and enhances the accumulation of a larger This area represents the westernmost, and most external, sector of
displacement along discrete shear planes (Aydin et al., 2006; Tondi the Sicilian orogenic belt, which is mainly comprised of south-
et al., 2006a). Mechanical twinning of calcite crystals (Ferrill and verging, Neogene fold-thrust tectonic elements (Fig. 1a; Scandone
Groshong, 1993) and precipitation of dissolved solids in the et al., 1974; Giunta et al., 2000).
nearby pores are processes also documented within deformation The most recent faults of NW Sicily (Nigro et al., 2000; Renda
bands in porous limestones (Tondi et al., 2006a; Tondi, 2007; Baud et al., 2000; Gueguen et al., 2002; Giunta et al., 2009) form a grid
et al., 2009; Vajdova et al., 2010; Rath et al., 2011). of high-angle strike-slip structures roughly oriented either W-NW
The transition from one deformation behavior to another (i.e. (right-lateral) or N-NE (left-lateral). The kinematics of these two
banding vs. faulting) is likely controlled by changes of the material sets of strike-slip faults is compatible to the current regional stress
properties within the bands; the resulting mechanical instability is field, which is characterized by a NW-SE oriented, greatest hori-
often accompanied by progressive evolution of the tectonic struc- zontal compression direction (Giunta et al., 2004; Tondi et al.,
tures (Aydin and Johnson, 1983; Shipton et al., 2005). In porous 2006b).
rocks, deformation first occurs in the form of single compactive At Favignana Island (Fig. 1b), deformed Triassic to Miocene
shear bands, evolves continuously forming zones of multiple platform carbonates, which pass upwards into deep-water marls
compactive shear bands and, eventually, faults composed of and limestones, are the basement units underlying Plio-Pleistocene
discrete, sharp, more or less planar discontinuities and fault rocks marine deposits (Abate et al., 1995, 1997; Incandela, 1995;
(i.e. breccia and gouge). Tavarnelli et al., 2003). These marine deposits are comprised of
The aim of this study is to investigate both dimensional Upper Pliocene shales overlain by 20e25 m thick, Lower Pleisto-
parameters and scaling relationships of single compactive shear cene carbonate grainstones (Fig. 1b).
bands, zones of compactive shear bands and strike-slip faults in
porous carbonate grainstones. Many excellent outcrops of Favig- 2.1. Lower Pleistocene carbonate grainstones
nana Island (Egadi Islands, western Sicily) expose a 21e23 m-thick
Lower-Pleistocene porous carbonate grainstones crosscut by the The yellowish carbonate grainstones of Favignana are Lower
aforementioned tectonic structures. There, we collected detailed Pleistocenic in age. The grainstones are characterized by beds
data related to length, thickness and amount of slip along struc- dipping: 5 e10 ESE, and a bed thickness ranging between 20 cm

tures as well as to investigate their detailed geometries, kinematics and 100 cm. The mean thickness of the whole Lower Pleistocene
and growth processes. Previous works on fault scaling relationships succession is nearly 21 m at Cala San Nicola and 23 m at Cala Rossa
provide a window into the mechanics of brittle strain localization in (Fig. 1b and Fig. 2). The maximum burial depth experienced by the
compact and porous rocks (Cowie and Scholz, 1992; Dawers et al., carbonate grainstones is estimated to be between 0 and 30 m
1993; Willemse et al., 1996; Scholz, 2002; de Joussineau and (Abate et al., 1995, 1997).
Aydin, 2007; Fossen et al., 2007; Schultz et al., 2008). In partic- Based upon their grain size, sorting, sedimentary/biogenic
ular, the previous data from porous rocks pertain primarily to structures and amount of matrix and cement, as well as the
displacementelength (DeL) and displacement-damage zone widespread erosional flooding surfaces, we distinguish up to seven
thickness (DeT) scaling relations of deformation bands in sand- different lithofacies (Fig. 2). In general, the carbonate grainstones
stones (Fossen and Hesthammer, 1997; Shipton and Cowie, 2001; are mainly comprised of bioclasts (i.e. Vermetus, Serpula, lamelli-
Wibberley et al., 2000; Shipton et al., 2005; and Fossen et al., banches, echinoids, algae and corals) ranging in size from sub-
2007 and the references therein). Data presented in this paper millimeter to centimeter (Fig. 2b). The amount of matrix and
provide a new insight into the evolution of statistical parameters of calcite cement vary significantly among the different lithofacies.
shear bands, which may be useful for an improved understanding Thin-section observations are consistent with presence of
of faults in porous carbonate rocks and characterization of intergranular and intragranular porosity within the carbonate
carbonate reservoirs (cf. Agosta et al., 2010). grainstones. Generally, well-developed intergranular pores form

Fig. 1. (a) Geological setting of western Sicily and (b) of Favignana Island. The location of the study area is marked with a black rectangle.