Texture analyses of ODP Site 131-808 sediments@en

The microfabric of 11 mudrock specimens from ODP Site 808 (Nankai accretionary prism) was quantitatively analyzed using X-ray texture goniometry and optical petrography. The objectives of the study were to learn about rock strain and to detect a component of bulk lateral shortening in the deformation of the mudstones. Strain evaluation is based on the predictions of March theory, and on distortions of initially homogeneous marker particle distributions (the Fry technique). The main results are as follows. The specimens underwent a strain path of progressive flattening, which is closely related to loss of pore space by vertical loading. A component of bulk lateral shortening is detectable in the top 550 mbsf at Site 808, but compared with the amount of uniaxial vertical shortening, its relative magnitude is probably small. Moreover, it cannot be said with confidence whether this is caused by toe contraction of the accretionary wedge or by gravitationally induced downslope movement of the sediment pile. The mudstones examined were deposited in a marine environment with an oxic bottom water column. […]本研究采用X射线织构测角法（X-ray texture goniometry）与岩相光学分析（optical petrography），对取自大洋钻探计划（Ocean Drilling Program, ODP）808站位（南海海沟增生楔，Nankai accretionary prism）的11件泥岩标本的微观组构（microfabric）开展了定量分析。本研究的目标为厘清泥岩变形过程中的岩石应变特征，并识别其中存在的整体侧向缩短组分。应变评估基于马奇理论（March theory）的预测结果，以及初始均匀分布的标记颗粒的畸变特征（弗莱法，Fry technique）。主要研究结果如下：所有标本均经历了递进压扁应变路径，该过程与垂向载荷引发的孔隙空间损耗密切相关。在808站位海底以下最上部550米（meters below sea floor, mbsf）的地层中可检测到整体侧向缩短组分，但与单轴垂向缩短量相比，其相对幅值大概率较小。此外，目前尚无法确切判断该侧向缩短是由增生楔的楔端收缩所致，还是由沉积体在重力作用下发生的顺坡移动引发。本次研究涉及的泥岩标本均沉积于底水层含氧的海洋环境中。[…]