Page 2 - RFP_2013_Cilona

and 30 m (Abate et al., 1995, 1997). Based upon their
grain size, sorting, sedimentary/biogenic structures and
amount of matrix and cement, as well as the widespread
erosional flooding surfaces, Tondi et al. (2012)
distinguished up to seven different lithofacies. In
general, the carbonate grainstones are mainly
comprised of bioclasts ranging in size from
submillimeter to centimeter. The amount of matrix and
calcite cement varies significantly among the different
lithofacies. Thin-section observations are consistent
with presence of well-connected intergranular and
intragranular porosity within the carbonate grainstones.
Tondi et al. (2012) documented a wide range of
porosity in the host rock, the values vary between 30
and 50% (helium pycnometer measurements).
The structures used in this study are deformation
bands similar to those reported by Tondi (2007) within
the marine deposits of Lower Pleistocene age, cropping
out in the coastal plain of Castelluzzo (NW of the
Island of Sicily).
Deformation bands (DB) are structures peculiar of
porous rocks and consist of mm- to-cm thick tabular
zones that accommodate shear and/or volumetric strain
(e.g. Aydin & Johnson, 1978; Antonellini & Aydin,
1994; Aydin et al., 2006). While many examples of
deformation bands are reported from siliciclastic
sediments (see Fossen et al., 2007 for a full review),
only a few examples are described in porous limestones
(Micarelli et al., 2006; Tondi et al., 2006; Tondi, 2007; amount of displacement) of the two sets of shear
Agosta et al., 2009; Rath et al., 2011; Cilona et al.,
2012; Rustichelli et al., 2012; Tondi et al., 2012).
Deformation bands are easily recognizable in the field
because of their lighter-color and positive relief with
Figure 1. Plot explaining why this article is the way it is (after Faultman, 1992). Figure 1: a) Geological
setting of western Sicily, the arrow points Favignana Island, b) Geological map of Favignana, the study area
is marked by the red box (after Tondi et al., 2012).
respect to the parent rocks. Individual DBs can solve
volumetric and/or shear strain (Aydin et al., 2006), pure
volumetric deformation can form either compaction or
dilation bands. Pure shear deformation determines the
formation of shear bands. When both types of strain
occur along individual bands, compactive (negative
volumetric component) and dilatant (positive
volumetric component) shear bands may form (Aydin
et al., 2006).
In carbonate rocks, during advanced stages of
deformation, dissolution for pressure may occur within
the already compacted bands, determining a grain-size
reduction (Tondi et al., 2006; Tondi, 2007). The
transition from banding to faulting behavior is likely
controlled by changes of the material properties within
the bands. Generally, single compactive shear bands
evolve continuously forming zones of multiple
compactive shear bands and, eventually, fault zones
(Tondi et al., 2006; Tondi, 2007; Tondi et al., 2012)
comprised of discrete and sharp slip surfaces and fault
rocks (i.e. breccia and gouge). Within carbonates, the
shearing across pre-existing stylolites facilitates the
accumulation of slip and formation of discrete shear
planes (Aydin et al., 2006; Tondi et al., 2006; Tondi,
2007).
At Cala San Nicola, Favignana, thanks to the
presence of many quarries, the geometry, kinematics,
and dimensional parameters (i.e. length, thickness and
structures have been characterized (Tondi et al., 2012).
The data have been collected at Cala San Nicola (Fig.1
b) by means of several scan lines and detailed structural
maps at a 1:1 scale.
Stanford Rock Fracture Project Vol. 24, 2013 E-2