Behavior and mechanism of wet-sediment deformation -A study using pore size distribution, anisotropy of magnetic susceptibility and SEM image-

湿泥沙变形的特征是，变形引起的应变和/或剪切不会延伸到固体颗粒或矿物的表面和/或内部，而是被孔隙吸收。因此，泥沙湿变形与孔隙水的脱水成正比，在沉积序列中起着重要的传热和物质收支作用。为了更好地了解湿泥沙的变形行为及其与泥沙孔隙度变化的关系，开展了这项研究。结果如下：1)在研究中，我研究了a)来自上中新统三浦群的Misaki组、日本中部第四纪弧-弧碰撞盆地的Ashigara组的一系列泥岩；b)日本西部物质输送矿床Amazon Fan的全圆形岩心样品，ODP155；以及c)来自冲绳岛曼都群Kayo组的页岩，但遭受了湿沉积变形。我测量了孔隙度(用孔分布…2)剪切面和构造混杂岩(三崎组、卡约组)的磁化率各向异性(AMS)数据表明，沉积物中颗粒和矿物的骨架明显应变，最大的孔隙坍塌，而中、小孔隙未被破坏。认为剪切带和断层部位的变形从颗粒骨架的变形扩展到孔隙水的脱水。3)在湿沉积物变形的流态化沉积物(三崎组、ODP样)中，孔隙尺寸趋于一定程度的集中，与流态化作用相关的大小和小孔隙消失。研究结果表明，湿泥沙变形与孔隙流体性质的关系表现为两个过程：a)变形是由孔隙流体压力增加引起的，如外部孔隙流体的注入；b)骨架直接受到外应力的应变。含水率、渗透率、孔隙度等物性条件很可能控制这一过程。较少

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 … More 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