Geotechnical properties of Lau Basin sediments

Distribution of pore space and degree of cementation appear to be the main factors controlling the permeability of sediments retrieved from the Lau Basin. The undisturbed microfabrics of two lithologies, nannofossil ooze and vitric sandy silt, commonly found at Holes 834A, 835A, 838A, and 839Aof Leg 135 were examined by scanning electron microscopy equipped with energy dispersive X-ray spectral analysis and image analysis systems. The results of these analyses were compared with laboratory determinations of porosity, grain-size distribution, and permeability on discrete samples from the same sediment depths. The permeability of the vitric sandy silt is 3-5 orders of magnitude higher than the nannofossil ooze samples. The porosity of nannofossil ooze ranges from 6% to 12% greater than the porosity of vitric sandy silt, which partially reflects the finer texture of nannofossil ooze. Although the correlation of higher porosity with lower permeability is not surprising, factors other than simply grain-size distribution must be invoked to explain the large differences in permeability found in these samples.孔隙空间分布与胶结程度，为控制从劳盆地（Lau Basin）获取的沉积物渗透性的主要影响因素。本研究借助配备能量色散X射线光谱分析（energy dispersive X-ray spectral analysis）与图像分析系统的扫描电子显微镜（scanning electron microscopy），对135航次（Leg 135）834A、835A、838A及839A钻井孔中常见的两种岩性——颗石藻软泥（nannofossil ooze）与玻质砂质粉砂（vitric sandy silt）的未扰动微组构开展了观测分析。将上述分析结果，与同沉积深度离散样品的实验室孔隙度、粒度分布及渗透性测定结果进行对比。结果显示，玻质砂质粉砂样品的渗透性较颗石藻软泥样品高出3至5个数量级；颗石藻软泥的孔隙度较玻质砂质粉砂高出6%至12%，这一差异一定程度上反映了颗石藻软泥具有更细的质地结构。尽管孔隙度越高渗透性越低的相关性并不出人意料，但仍需引入粒度分布以外的其他因素，方能解释本研究样品中渗透性的显著差异。