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

湿沉积物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，而是在孔隙中被吸收。因此，湿沉积变形与孔隙水的脱水具有正相关关系，在沉积演替中的传热和物质收支中起着重要作用。为了更好地了解湿质沉积物的变形行为及其与孔隙度变化的关系，开展了本研究。结果如下图所示：1)在研究中，我考察了a)上中新世三浦群Misaki组的一系列泥岩；日本中部第四纪弧-弧碰撞盆地石原群；b)亚马逊扇西部块体搬运矿床全圆岩心样品，ODP leg155；c)页岩，但受到湿沉积变形的影响，产自冲绳岛东群加约组。用压汞式孔隙度仪测量孔隙度（孔隙分布和More n型）、x射线CAT扫描图像和磁化率各向异性（AMS）。2)剪切面和构造混杂岩（Misaki组、Kayo组）的AMS数据表明，沉积物中颗粒和矿物的骨架发生了明显的应变，最大孔隙发生了崩塌，而中、小尺寸孔隙没有被破坏。认为剪切带和断裂部位的变形源于颗粒骨架的变形，并由骨架的变形扩展到孔隙水的脱水。3)在流态化沉积物（Misaki组，ODP样品）中，由于沉积物湿变形，孔隙尺寸在一定程度上趋于集中；小孔和大孔随着流化而消失。结果表明，孔隙流体压力的增加是导致骨架变形的流化作用的主要原因。研究结果表明，湿沉积变形与孔隙流体行为的关系表现为两个过程：a)孔隙流体压力的增加（如外部孔隙流体的注入）引起变形；b)外部应力直接使框架变形。物性条件如含水率、渗透率、孔隙度等，都有可能控制这一过程。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