Page 10 - Tondietall2015

Italian Journal of Geosciences Accepted manuscript

ranging between 50° and 80°, and ii) a younger set of right-lateral strike-slip faults striking E-W
with an almost vertical dip (TONDI et alii, 2006; fig. 4b). These faults likely developed at a depth
shallower than 0.5 km (~10 MPa overburden; CILONA et alii, 2012), during the syn- and post-tilting
deformation phases recorded in the Majella anticline (TONDI et alii, 2006).

According to TONDI et alii (2006), faults are due to shearing of stylolites that previously
localized along and within former compactive shear bands. The displacement along faults is
between 10 and 90 cm. The fault cores, here called Zone I (sensu TONDI, 2007) are rock volumes
characterized by fine-grained cataclastic fault rocks (breccia or gauge) including several slip
surfaces (fig. 2b). Under the microscope fault cores appear as zones of grain size and porosity
reduction, made of comminuted grains embedded within dark insoluble organic matter (Zone I of
TONDI, 2007). Porosity is less than 1%. The surrounding compactive shear bands, analogue to the
Zone II (sensu TONDI, 2007), are characterized by a reduced porosity (1-4%) but not grain size
reduction occurred. No porosity reduction induced by calcite precipitation (Zone III of TONDI,
2007) is documented in the carbonates surrounding the bands.

The former compactive shear bands formed by particulate flow involving grain translation and
rotation with pore collapse, resulting in a tight band with a noticeable shear displacement gradient
but without significant grain breakage (TONDI et alii, 2006). Grain size reduction occurred solely by
the pressure solution processes and the resulting discrete stylolites, and their subsequent shearing
accompanied by cataclasis.

PERMEABILITY MEASUREMENTS
The air-permeability measurements were made across nine fault zones: five affecting the
Favignana carbonate grainstones and four the Majella ones (Table 1). Selected fault zones are
representative of the various sets described in the previous section, and range in displacement from
10 to ~200 cm (figs. 6 and 7).