Page 15 - Tondietall2015

Italian Journal of Geosciences Accepted manuscript

compactive shear bands, show normal to strike-slip kinematics and range in displacement from 10
to ~200 cm.

Permeability measurements revealed a sharp permeability reduction, roughly two orders of
magnitude, moving from host rock to cataclastic fault cores through damage zones in both studied
grainstones. The measured permeability reduction follows a power law trend quite similar to that
documented for porosity. Meaningful relationships are found between the deformation processes
previously documented for the study fault zones and the measured permeability. The carbonate
grainstones in the fault damage zones record non-destructive compactive granular flow
accompanied by pore collapse, and possible precipitation of calcite cement, which determined a
reduced porosity and pore connectivity but a small decrease of permeability relative to the host
rock. On the contrary, within the fault cores, the extensive pressure solution that took place and a
switch of deformation, which evolved from particulate flow to compactant cataclastic flow, caused
a progressive grain size reduction, an increase of the silt- and clay-size fractions amounts, and
therefore a pronounced porosity and permeability reduction.

Moreover, the surprising result of this study is the remarkable difference in air-permeability
values documented for the two host rocks, suggesting the key role played by the pore dimensions,
as well as the effective porosity, on the permeability values of the faulted porous carbonate
grainstones. Finally, the results of this study reveal that fault-related processes dramatically affect
the overall permeability of porous carbonate grainstones. The related geofluid circulation paths thus
depend on orientation, frequency and connectivity of the sub-seismic resolution fault zones. A key
role on the overall permeability of faulted porous carbonate reservoirs/aquifers is played by the
original pore network characteristics of the host rocks.

ACKNOWLEDGEMENTS
We thank Sandro Conticelli (the Editor-in-Chief of the Italian Journal of Geosciences), an
anonymous Associate Editor, Sergio Vinciguerra and Shang Deng for their constructive and