Correlation of fracture patterns, lithology and tectonic position in Mesozoic carbonate rocks

Analyzing core data for fracture analysis is restricted by costs and gives limited information. Outcrop studies with the software DigiFract give a more complete set of information about fractures. The aim of this research is to find correlations between fractures patterns, lithology and tectonic position in the area around Coldigioco, Marche, Northern Apennines, Italy. In this area the current topography consists of two anticlinal structures with thrust origins. These thrusts originated during the Miocene as a result of the Corso-Sardinia-Calabria/Adria collision. The formations in this region consist of limestone and some chert/marl layers. To analyze the fracture patterns there are different ways of statistical processing, including determining fracture density, fracture orientation, fracture height and mechanical unit distributions. By correlating these statistics with lithology and tectonic location, the following can be concluded: The difference in fracture densities between the eastern and western flanks of the eastern anticline are caused by an active axial surface fold. The dense fractured western flank of the anticline is part of a deformed panel and the less dense fractured eastern flank is part of a undeformed panel of the fold. Furthermore one could conclude that the fracture pattern in the undeformed panel of the fold tends to be irregular due to the presence of an axial plane just above this panel. Parts of this panel have already been influenced by this upcoming change of bedding orientation or some parts have already passed this axial plane. The final conclusion related to tectonic position is that on the axial plane of a fold compressive stresses can cause stylolites perpendicular to the bedding. Two prominent influencing factors in lithology are the hardness of the rock and the presence of marl and chert layers. The formations of middle hardness are fractured regular. The opposite can be seen in the other, harder or softer formations. Finally one can conclude that marl and chert layers act as non-fractured or less fractured boundaries and cause bed confined fractures.