5:15 PM - 6:45 PM
[SEM13-P08] Magnetic characteristics related to consolidation in sedimentary soft rocks
Keywords:Consolidation, Magnetic characteristics, Sedimentary soft rocks
Magnetic minerals contained in sediments are aligned in the direction of the earth's magnetic field at a depth of approximately 15-40 cm from the seafloor surface, after that, clay minerals become oriented in consolidation and diagenesis. At the tectonic margin, both overburden pressure and compressive stress are added to rocks in the consolidation process. These re-arrangements of the mineral particles affect the orientation of the magnetic minerals. Inclination error in paleomagnetic directions was confirmed in unconsolidated deposits such as marine sediment and the equations have already been suggested to correct the error. However the detailed mechanism of how the residual magnetization vector changes with the degree of consolidation remains largely unknown.
In this study, the anisotropy of initial magnetic susceptibility (AMS) and anhysteretic remanent magnetization (ARM) were measured before and after the consolidation test to clarify how the magnetic properties change by consolidation. Using siltstones taken from the Mio–Pleistocene forearc basin in the Boso Peninsula, central Japan, the specimens were formed; diameter and height are approximately 25 and 20 mm, respectively. These specimens were consolidated using the uniaxial compression system with a consolidation ring and the maximum compression stress is 80 MPa.
As a result, the initial magnetic susceptibility revealed that the maximum axis changes in a direction closer to horizontal when the direction of consolidation is oblique to the maximum axis of an anisotropic ellipsoid. The Flynn diagram confirmed that the degree of the plane structure increased after the consolidation when the direction of consolidation was perpendicular to the maximum axis of the anisotropic ellipsoid. ARM measurements show that the remanent magnetization decreases in the direction parallel to the consolidation direction. It is consistent with the increase in the degree of the plane structure shown in the Flynn diagram.
In this study, the anisotropy of initial magnetic susceptibility (AMS) and anhysteretic remanent magnetization (ARM) were measured before and after the consolidation test to clarify how the magnetic properties change by consolidation. Using siltstones taken from the Mio–Pleistocene forearc basin in the Boso Peninsula, central Japan, the specimens were formed; diameter and height are approximately 25 and 20 mm, respectively. These specimens were consolidated using the uniaxial compression system with a consolidation ring and the maximum compression stress is 80 MPa.
As a result, the initial magnetic susceptibility revealed that the maximum axis changes in a direction closer to horizontal when the direction of consolidation is oblique to the maximum axis of an anisotropic ellipsoid. The Flynn diagram confirmed that the degree of the plane structure increased after the consolidation when the direction of consolidation was perpendicular to the maximum axis of the anisotropic ellipsoid. ARM measurements show that the remanent magnetization decreases in the direction parallel to the consolidation direction. It is consistent with the increase in the degree of the plane structure shown in the Flynn diagram.