The role of deformation bands, stylolites and sheared stylolites in fault development in carbonate grainstones of Majella Mountain, Italy

In this paper we document deformation processes in porous carbonate grainstones of Cretaceous age in Majella Mountain in the central Apennines of Italy by detailed mapping of meso- and microstructural features as well as thin section observations and image analyses. We distinguished three main deformation mechanisms: (i) deformation bands developed by compaction and shear strain localization, (ii) stylolites formed by pressure solution, and (iii) subsequent shearing of stylolites. The deformation bands occur in six sets: five sets are compactive shear bands at high angles to bedding and one, which is the oldest, occurs parallel to bedding and is interpreted to be a compaction band. Stylolites localize along and within all six sets of deformation bands and are commonly sheared, as evidenced by striated surfaces and detectable offsets. These sheared stylolites are in many cases associated with one or two sets of subsidiary stylolites, oblique to the major set. The band-parallel sheared stylolites, together with the associated oblique sets of stylolites, form a tabular zone of fine grained cataclastic material within the compactive shear bands and accommodate slip in the range of 5–75 cm. The bed-parallel compaction bands and bed-parallel stylolites, which are kinematically compatible, are interpreted to be pre-tilting structures developed in response to the overburden, whereas the five sets of compactive shear bands and the associated stylolites and sheared stylolites likely occurred during the syn- and post-tilting deformation phases recorded in the Majella anticline.