(Table 3) Physical properties of DSDP Hole 72-515A

Hole 515A was drilled in the southern Brazil Basin by the Glomar Challenger on DSDP Leg 72, using the newly developed hydraulic piston corer (HPC). A total of 108 m of undisturbed terrigenous mud (T1) and sandy mud (T2) was obtained (see site chapter, Site 515, this volume). The core was sampled at levels that corresponded to 50-kPa increments of overburden pressure to determine if a pattern of clay fabric development could be discerned. After criticalpoint drying and gold-palladium coating, 15 samples were analyzed with a scanning electron microscope (SEM).
Clay fabric consists of randomly oriented, large and small domains of face-to-face (FF) stacked clay particles, frequently linked together by short "chains" in an edge-to-face (EF) orientation. As overburden pressure increases, linkages decrease, and the "chains" become incorporated into the domains. Distortion of platelike domains into "cornflake" structures (well-crystallized montmorillonite?) and spherical aggregates occurs at overburden pressures of 400 kPa. Orientation parallel with bedding occurs at 500 kPa as the "cornflake" structures become flattened and compressed.
Maximum fabric development occurs at 590 kPa. Large plates and coalesced domains form a pervasive linear FF pattern, interrupted by a few large and small EF bridging structures. Deformation of the large EF-oriented plates occurs, forming circular, pitlike voids.
Fabric development in cores from this deep-sea site follows well the developmental model suggested by Bennett and others (1981) for Mississippi Delta clays with high to medium void ratios.

本数据集涉及的515A孔由格洛玛·挑战者号（Glomar Challenger）钻探船于深海钻探计划（Deep Sea Drilling Project, DSDP）第72航次在巴西南部盆地钻取，作业中采用了新研发的液压活塞取芯器（hydraulic piston corer, HPC）。本次钻探共获取总长108米的未受扰动陆源泥（T1）与砂质泥（T2）岩芯（详见本卷515站位章节）。为明确黏土组构的发育模式是否可被识别，研究人员按上覆压力每递增50千帕的间隔对岩芯进行分层取样。经临界点干燥与金钯镀膜处理后，使用扫描电子显微镜（scanning electron microscope, SEM）对15个样品开展分析。

黏土组构由随机定向的、大小不一的面-面（face-to-face, FF）堆叠黏土颗粒域构成，这类颗粒域常通过边-面（edge-to-face, EF）取向的短“链状”结构相互连接。随着上覆压力升高，这类连接结构逐渐减少，“链状”结构逐渐融入颗粒域中。当上覆压力达到400千帕时，板状颗粒域会变形为“玉米片”结构（结晶度良好的蒙脱石？）并形成球状团聚体。当压力升至500千帕时，“玉米片”结构被压扁压实，黏土颗粒开始形成与层理平行的定向排列。

当压力达到590千帕时，黏土组构发育达到顶峰。大尺寸板状颗粒与融合的颗粒域形成了广泛分布的线性面-面堆叠结构，仅少量大小不一的边-面桥接结构会打断该结构。带有边-面取向的大尺寸板状颗粒发生变形，形成圆形坑状孔隙。

该深海站位岩芯中的黏土组构发育过程，完全契合Bennett等人（1981）针对中高孔隙率密西西比三角洲黏土提出的组构发育模型。