Page 12 - Tondietall2015

Italian Journal of Geosciences Accepted manuscript

distribution (fig. 3b) of the two studied carbonates we suggest that the permeability differences are
also determined by the characteristics of the pore network (especially the overall pore dimensions)
in the two grainstones. The Favignana grainstones, indeed, are characterized by a well-connected
network of large intergranular pores, whilst the pore space in the Orfento grainstones is dominated
by micro-porosity (fig. 3b). Due to these characteristics it is likely that the connectivity of the
Orfento porosity is lower and the pore throats are much more tortuous. The difference in pore
structure is a consequence of an overall lower grain size and tighter texture (likely due to the higher
overburden loading) of the Orfento grainstones with respect to the Favignana one, and is also
influenced by the fossils type and amount. There is about one order of magnitude difference
between the pore throats in the Orfento Fm and the Favignana grainstones (fig. 3b). The two host
rocks show porosity difference of up to 15-20%, moreover the presence of a significant amount of
submicron pores in the Orfento Fm. may contribute to the observed permeability differences.
Indeed, the contribution of those pores to permeability becomes negligible if compared to that one
of larger pores. The porosity decrease between the two host rocks and the respective fault cores,
around two orders of magnitude, is similar to what measured previous authors on naturally-
deformed carbonates (RATH et alii, 2011; ANTONELLINI et alii, 2014); conversely measurements
performed of laboratory-deformed grainstones (CILONA et alii, 2012) showed half an order of
magnitude difference.

As well as for the porosity, both grainstones show approximately two order of magnitude
permeability decrease between the host rocks and the cataclastic fault cores. Also ANTONELLINI et
alii, (2014) measured the same ratio between host rock and cores in the grainstones of S. Vito Lo
Capo (NW Sicily), which are equivalent to the Favignana grainstones. Conversely, RATH et alii
(2011) documented a decrease of four orders of magnitude between the host rock and the
deformation bands in carbonate grainstones cropping out in western Austria.