Abstract
A deformation model is presented, which explains the distribution and type of fracturing in the Vila Velha Sandstones, outcropping in eastern border of Parana Basin, south Brazil. The studied sedimentary section consists of shallow sub aqueous sandstone lobes of the Campo Mourao Formation, Itarare Group, deposited in a periglacial environment. The study was based on detailed description of outcrops, interpretation of aerial photos and structural analysis of fractures and structural blocks. The sandstones occur as sub horizontal beds, tilted apart from large faults. Deformation bands, zones of deformation bands and slip planes are the recognized structural elements affecting sandstones, which are probably associated to a regional fault zone evolution. The fracture system is conjugated, striking mainly to N10-20E and N60-80W. Fracture induced permeability is inferred from large and small-scale structures in outcrops, where the wall rocks are oxidized and silicified close to slip planes. This situation suggests that the fractures functioned as conduits during its formation, being transformed to barriers to fluid migration after mineral precipitation.
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