Fault-related solution cleavage in exposed carbonate reservoir rocks in the Southern Apennines, Italy

The deformation associated with a number of kilometre-scale strike-slip fau lt zones which cut through outcropping carbonate rocks in the Southern Apen nines was investigated at regional and outcrop scales. These faults trend r oughly east-west and were studied at the Gargano Promontory on the Adriatic Coast tin the Apulian foreland and in the Matese Mountains, about 120 km t o the west (within the Apenninic fold-and-thrust belt). The fault zones are 200-300 m wide and typically comprise a core surrounded by a damage zone. Within fault cores, fault rocks (gouges and cataclasites) typically occur a long master slip planes; in damage zones, secondary slip planes and solutio n cleavage are the most important planar discontinuities. The protolith car bonates surrounding the fault zone at Gargano show little deformation, but they are fractured in the Matese Mountains as a result of an earlier thrust phase. Cleavage surfaces in the damage zone of the studied faults are interpreted to be fault propagation structures. Our field data indicate that cleavage-f ault intersection fines are parallel to the normals of fault slip-vectors. The angle between a fault plane and the associated cleavage was found to be fairly constant (c. 40 degrees) at different scales of observation. Finall y, the spacing of the solution cleavage surfaces appeared in general to be regular (with a mean of about 22 mm), although it was found to decrease sli ghtly near a fault plane. These results are intended to provide a basis for predicting the architecture of fault zones in buried carbonate reservoirs using seismic reflection and borehole data.