(Table 1) Porosity measurements, median pore diameter of pore sizes and volume fractions of bulk sediment from different Holes of IODP site 333@en

Microporosity by performing low pressure nitrogen adsorption measurements on 13 shallow marine mudstone samples from the Nankai Trough offshore Japan. The samples were from two reference Sites on the incoming Philippine Sea Plate, and one Site above the accretionary prism. I determined pore size distributions using the Barrett–Joyner–Hallenda (BJH) model, and merged these with existing mercury injection capillary pressure (MICP) measurements to construct a full distribution covering micro- to macropores. I found that overall pore sizes decrease with consolidation, and that microporosity content (pores < 2 nm in diameter) is influenced mainly by mineralogy, with some influence of diagenetic processes. A small amount of microporosity (~ 0.25% of bulk sediment volume) is present in these sediments at the time of burial, presumably contained mainly in clays. Additional microporosity may develop as a result of alteration of volcanic ash at the reference Sites, and may be related to diagenetic processes that create zones of anomalous high porosity. Comparisons with porewater chemistry (K+, Ca2 +, Sr, Si) show inconsistent relationships with microporosity development and cannot confirm or deny the role of ash alteration in this process. The strongest correlation observed at the three Sites was between microporosity volume and clay mineral fraction. This suggests that microporosity content is determined mainly by detrital clay abundance and development of clay as an ash alteration product, with some contribution from amorphous silica cement precipitated in the zones of anomalous high porosity.本研究针对日本近海南海海槽的13件浅海相泥岩样品开展低压氮气吸附测试，以表征其微孔孔隙度特征。这些样品分别采自菲律宾海板块俯冲带的两个参考站位，以及增生楔上方的一个站位。本研究采用Barrett-Joyner-Hallenda（Barrett–Joyner–Hallenda, BJH）模型计算孔径分布，并将其与已有的压汞毛细管压力（mercury injection capillary pressure, MICP）测试数据进行整合，构建覆盖微孔至大孔的完整孔径分布曲线。研究发现，随固结程度升高，整体孔径呈减小趋势；微孔孔隙度（直径小于2 nm的孔隙）主要受矿物组成影响，成岩作用亦存在一定调控作用。埋藏初期的沉积物中即存在少量微孔孔隙度（约占沉积物总体积的0.25%），其主要赋存于黏土矿物中。参考站位处的火山灰蚀变作用可形成额外的微孔孔隙度，该过程可能与形成异常高孔隙带的成岩作用相关。通过与孔隙水化学组分（K+、Ca2+、Sr、Si）进行对比分析，发现其与微孔孔隙度发育的相关性并不一致，无法证实或否认火山灰蚀变在该过程中的作用。在三个站位中，相关性最显著的为微孔孔隙体积与黏土矿物组分占比之间的关系。这表明微孔孔隙度主要受陆源黏土丰度以及作为火山灰蚀变产物的黏土矿物发育程度控制，异常高孔隙带中沉淀的无定形硅质胶结物亦存在一定贡献。