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Morphology of the pore space in claystones – evidence from BIB/FIB ion beam sectioning and cryo-SEM observations
1Geologie – Endogene Dynamik, RWTH Aachen University, Lochnerstr. 4–20, 52056 Aachen, Germany
2Geological Institute, RWTH Aachen University, Wüllnerstr. 2, 52062 Aachen, Germany
Abstract. The morphology of pore space has a strong effect on mechanical and transport properties of mudrocks and clay-rich fault gouge, but its characterization has been mostly indirect. We report on a study of Boom clay from a proposed disposal site of radioactive waste (Mol site, Belgium) using high resolution SEM at cryogenic temperature, with ion beam cross-sectioning to prepare smooth, damage free surfaces. Pores commonly have crack-like tips, preferred orientation parallel to bedding and power law size distribution. We define a number of pore types depending on shape and location in the microstructure: large jagged pores in strain shadows of clastic grains, high aspect ratio pores between similarly oriented phyllosilicate grains and crescent-shaped pores in saddle reefs of folded phyllosilicates. 3-D reconstruction by serial cross-sectioning shows 3-D connectivity of the pore space. These findings offer a new insight into the morphology of pores down to nano-scale in comparison to traditional pore size distributions calculated from mercury Injection experiments, explain slaking of clays by successive wetting and drying and provide the basis for microstructure-based models of transport in clays.
Final Revised Paper (PDF, 14535 KB) Discussion Paper (eED)
Citation: Desbois, G., Urai, J. L., and Kukla, P. A.: Morphology of the pore space in claystones – evidence from BIB/FIB ion beam sectioning and cryo-SEM observations, eEarth, 4, 15-22, 2009. Bibtex EndNote Reference Manager
