Although anomalous compaction (dramatic physical property changes) is widely recognised from scientific drilling of sections of marine biosiliceous sediments that have undergone silica diagenesis, the precise mechanisms governing vertically abrupt compaction are poorly understood. To better understand relationships between silica diagenesis and anomalous compaction, the microfabric and composition of hemipelagic sediments at the Ocean Drilling Program Sites 794 and 795 in the Sea of Japan were analysed in detail. Textural and mineralogical examination of core samples from these stations shows that dissolution of opal-A and precipitation of opal-CT are the two major controls on anomalous compaction. Other observed components of the diagenetic history, such as structural ordering of diagenetic opal and precipitation of authigenic phases (clay minerals and pyrite) do not strongly affect physical properties. Above the opal-A to opal-CT transition zone (anomalous compaction interval), opal-A deposits impart significant porosity to the sediments. Because of this high porosity and the relative incompressibility of siliceous tests, normal mechanical compaction of biosiliceous units is retarded and mainly postdates silica diagenesis. Across the transition zone, a sharp reduction in opal-A content under dissolution (from 35 to ~12% in Site 794 and from 45 to 7% in Site 795) leads to a significant reduction in sediment framework stability, which makes it vulnerable to sudden collapse, abrupt reduction in intergranular and intragranular porosity (and increasing bulk density), and a decrease in pore-water content. Although later opal-CT precipitation does influence the petrophysical response, mineralogical analyses suggest a lesser role for opal-CT precipitation on host porosity than precursor opal-A dissolution. This is attributed to the inhibiting effects of high abundance of clay-sized components that have restricted significant precipitation of opal-CT.

尽管通过科学钻探已经经历了二氧化硅成岩作用的海洋生物硅质沉积物的断面，人们普遍认识到异常压实（剧烈的物理性质变化），但对垂直垂直压实的精确机理却知之甚少。为了更好地了解二氧化硅成岩作用与异常压实之间的关系，详细分析了日本海海洋钻探计划站点794和795中的半沉积沉积物的微结构和组成。对来自这些站点的核心样品的组织学和矿物学检查显示，蛋白石A的溶解和蛋白石CT的沉淀是异常压实的两个主要控制因素。成岩史的其他观察到的成分，例如成岩蛋白石的结构排序和自生相（粘土矿物和黄铁矿）的沉淀不会强烈影响物理性能。在蛋白石A到蛋白石CT的过渡带上方（异常压实间隔），蛋白石A的沉积物赋予沉积物很大的孔隙度。由于这种高孔隙度和硅质测试的相对不可压缩性，生物硅质单元的正常机械压实受到阻碍，并且主要推迟了二氧化硅的成岩作用。在整个过渡带，溶解时蛋白石A含量急剧下降（在794号站点从35％降低到〜12％，在795号站点从45％降低到7％）导致沉积物骨架稳定性的显着降低，这使其很容易受到侵蚀。突然崩塌，颗粒间和颗粒内孔隙率突然降低（并增加了堆积密度），并减少孔隙水含量。尽管后来的蛋白石CT沉淀确实会影响岩石物性响应，但矿物学分析表明，蛋白石CT沉淀对宿主孔隙度的作用要小于蛋白石A的前驱体溶解作用。这归因于高含量的粘土尺寸组分的抑制作用，这些组分限制了蛋白石-CT的大量沉淀。