The evolution of a model trap in the central Apennines, Italy: Fracture patterns, fault reactivation and development of cataclastic rocks in carbonates at the Narni Anticline
F. Storti et F. Salvini, The evolution of a model trap in the central Apennines, Italy: Fracture patterns, fault reactivation and development of cataclastic rocks in carbonates at the Narni Anticline, J PETR GEOL, 24(2), 2001, pp. 171-190
Recent hydrocarbon discoveries in the Southern Apennines of Italy have focu
ssed attention on the importance of studying fracturing and cataclasis in c
arbonate rocks because of their fundamental impact on reservoir permeabilit
y and connectivity The Narni Anticline in the central Apennines consists of
a stack of easterly-verging carbonate thrust sheets compartmentalized by e
xtensional and strike-slip fault zones. The structure provides afield analo
gue for studying the evolution of superimposed fold-and-fault-related fract
ures in carbonate reservoir rocks.
The fracture pattern at the Narni Anticline developed as a result of three
mechanisms. (a) layer-parallel shortening predating folding and faulting; (
b) thrust-related folding and further thrust breakthrough; and (c) extensio
nal and strike-slip faulting. Along-strike (longitudinal) fractures develop
ed during progressive rollover fault-propagation folding, and their intensi
ty depends on the precise structural position within the fold: fracture int
ensity is high in the forelimb and low in the crest. The 3-D architecture o
f the mechanical anisotropy associated with thrusting folding and related f
racturing constrained the location and geometry of subsequent extensional a
nd strike-slip faulting. The superimposition in damage zones of a fault-rel
ated cleavage on the pre-existing fracture pattern, which is associated wit
h layer-parallel shortening and thrust-related folding, resulted in rock fr
agmentation and comminution, and the development of cataclastic bands.
The evolution of fracturing in the Narni Anticline, its role in constrainin
g thrust breakthrough trajectories and the location of extensional and stri
ke-slip faults, and the final development of low-permeability cataclastic b
ands, will be relevant to studies of known oilfields in the Southern Apenni
nes, as well as for future exploration.