2:45 PM - 3:00 PM
[MIS17-05] Microstructure of siltstones in the Mio-Pleistocene forearc basin indicated by anisotropy of physical and mechanical properties
Keywords:Siltstone, Anisotropy, Pysical properties, Mechanical properties, Sedimentary basin
Increasing overburden pressure proceeds with consolidation in sedimentary basins, and mineral particles in sediments are arranged by the overburden pressure during the consolidation process. The arrangement of mineral particles forms the microstructure of sedimentary rocks, however, it is difficult to get information about the microstructure of siltstone and mudstone composed of minute particles by visual observation. On the other hand, the arrangement of mineral particles related to the bedding plane affects the physical properties of sedimentary rocks. We measured the physical and mechanical properties of siltstone in the sedimentary soft rocks and discussed the microstructure of siltstone using the anisotropy of these properties. Using the siltstone taken from the Mio–Pleistocene forearc basin in the Boso Peninsula, central Japan, elastic wave velocity, thermal conductivity, electrical conductivity, tensile strength, and consolidation yield stress were measured to estimate the degree of anisotropy. The measurements were performed using three different directions to the bedding plane.
Elastic wave velocity, thermal conductivity, and electrical conductivity of the parallel direction to the bedding plane were larger than those of the perpendicular to the bedding plane, and the tensile strength showed a clear weakness in the perpendicular to the bedding plane. The degree of anisotropy in the physical properties decreased as the porosity decreased from 60% to 35%, which differs from the anisotropy in the sedimentary rocks with porosity less than 35%. In addition, the arrangement of mineral particles relative to the bedding plane indicated by the physical and mechanical properties showed different characteristics depending on the geological structure. The siltstones taken from the monocline basin showed relatively greater anisotropy than the siltstones taken from the folded basin, and the anisotropy of the folded basin changed based on folding.
Elastic wave velocity, thermal conductivity, and electrical conductivity of the parallel direction to the bedding plane were larger than those of the perpendicular to the bedding plane, and the tensile strength showed a clear weakness in the perpendicular to the bedding plane. The degree of anisotropy in the physical properties decreased as the porosity decreased from 60% to 35%, which differs from the anisotropy in the sedimentary rocks with porosity less than 35%. In addition, the arrangement of mineral particles relative to the bedding plane indicated by the physical and mechanical properties showed different characteristics depending on the geological structure. The siltstones taken from the monocline basin showed relatively greater anisotropy than the siltstones taken from the folded basin, and the anisotropy of the folded basin changed based on folding.