| Research Abstract |
Characteristic feature of wet sediment deformation is that strain and/or shear due to deformation does not extend to surface and/or interior of solid particle or mineral, and is absorbed within pore. Hence, wet sediment deformation has positive relationship to dewatering of pore water and it plays an important role in heat transfer and material budget in sedimentary succession. This study was carried out in order to better understand behavior of wet sediment deformation and its mechanism in relation to porosity change of the sediment. Results were shown as bellows :
1) In the study, I examined a) a series of the mudstones obtained from the Misaki Formation, Upper Miocene Miura Group ; the Ashigara Group, Quaternary arc-arc collision basin, central Japan ; b) whole round core sample of the Western mass transport deposit, Amazon Fan, ODP leg155 ; and c) shale but suffered wet sediment deformation, from the Kayo Formation, Shimanto Group, Okinawa. I measured porosity (with pore distributio
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n pattern by mercury injection-type porosimeter) , X-ray CAT scan image and anisotropy of magnetic susceptibility (AMS) .
2) AMS data from shear plane and tectonic melange (Misaki Formation, Kayo Formation) show that framework of particles and minerals in the sediment is significantly strained, and the largest pore is collapsed whereas the moderate size and small size pore is not broken. It is suggested that the deformation of shear zone and fault place from the deformation of the framework of particles, and extends to pore water dewatering as result of the deformation of the framework.
3) In the fluidized sediments (Misaki Formation, ODP sample) due to wet sediment deformation, the pore size tends to be concentrated within some extent ; the small and large pore was disappeared associated with fluidization. It suggests that the fluidization which deforms the framework was taken place by increase of pore fluid pressure.
Rrsults of this study tell us that the relation between wet sediment deformation and behavior of pore fluid shows the two processes : a) deformation was caused by increase of pore fluid pressure, e.g.due to injection of external pore fluid, and b) the framework was strained directly by external stress. Condition of physical property such as water content, permeability porosity and so on, is likely to control the process. Less
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