Petrographic quantification of brecciated rocks by image analysis. Application to the interpretation of elastic wave velocities

This paper presents a new procedure to quantify the petrology of materials with complex and heterogenic rock-fabric features. The classical methodologies for petrographic quantification by image analysis are not appropriate for this kind of rock due to both the high chromatic complexity of these materials and the scale with which the samples are studied. The proposed process is particularly interesting for materials with complex chromatic characteristics such as highly fractured rocks, concrete, etc. Two commercial varieties of highly fractured (brecciated) dolostones were selected for this study in order to test the designed methodology.This new procedure is based on the analysis process of colour images obtained from mesoscopic sample scanning. Six petrographic parameters and diagrams have been designed in order to quantify the most influential aspects in compressional (vp) and shear (vs) ultrasonic wave propagation. These petrographic parameters and diagrams are: brecciation density, brecciation density map, clast size distribution, fine-grained matrix content, shape-preferred orientation and rose diagrams.The results demonstrate that the proposed methodology is suitable for quantifying the petrography of these kinds of materials. Furthermore, the variations measured in vp and vs are fully explained by the values measured for the following parameters: brecciation density, fine-grained matrix content, clast size distribution and preferred orientation of clasts.