IAMG 2001--Cancún Technical Program--Session N

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Fractal Analysis of Mineral Weathering-Toward Quantitative Approach by Klaudia Oleschko*, Universidad Nacional Autónoma de México, Instituto de Geología, Mexico, Jean-Francois Parrot, IRD, Paris, France, and Taud Hind, Instituto de Geografía, UNAM, México Weathering has became the state-of-the-art issue due to general concern about its influence on the CO2 budget and, possibly, on the climatic changes. However, in spite of the different qualitative and semi-quantitative methods developed during the last three decades, the description and classification of mineral and rock weathering still remains confuse, showing a lack of agreement between geologists. We used the fractal approach in order to design the unbiased quantitative weathering assessment, being universal, easy to apply, precise and scale independent. The measurements are performed locally on gray tone images using an adaptive box-counting technique,calculating the local fractal dimension of each pixel inside a sliding cube. The designed procedure is similar to Digital Elevation Model. In both approaches the image is viewed in a three dimensional space, using a gray level (image texture analysis) or the altitude (surface roughness modeling) as a third dimension. A local fractal dimension show to be able to detect the image textural and structural features, extracting weathering ones independently of the illumination conditions. In the present research, the strong statistical self-similarity, extending to over 4 decades of length scales, was documented for pore and solid sets of two common silica minerals of contrasting origin: quartz and biogenic A-opal (phytolites). The fractal parameters (P) were precise measures of the heterogeneity of solid and pore distribution across the mineral surface (P1), the degree of grain weathering (P2), the rugosity of solid/pore interface (P3) and the continuity and tortuosity of solid and pore patterns (P4).