【摘要】 对取自IODP 311航次(东北太平洋Cascadia大陆边缘)所有5个站位、采样间距约为1.5m的614件沉积物样品,利用Beckman Coulter LS-230激光粒度仪进行了沉积物粒度分析,获得了沉积物粒度随深度变化特征,进而与水合物层位的替代指标进行了位置对比,这些指标包括特殊沉积构造(soupy和mousse-like构造)、测井数据(LWD)推算出来的水合物饱和度(Sh)、岩芯红外图像和实际钻取的含水合物沉积物等。发现沉积物粒度分别为31～63μm和63～125μm的2组较粗粒径的沉积物数量变化增多的位置与水合物出现层位之间存在较好的位置对应关系。如在U1326站位海底以下5～8m、21～26m、50～123m、132～140m、167～180m、195～206m、220～240m深度位置出现了沉积物粒度明显偏向粗粒的趋势,而这些位置正好对应于大多数特殊沉积构造出现的深度,也对应于水合物饱和度(Sh)值相对较高的深度,并与一些实际钻取的赋含水合物的浊积沙层观察结果一致。因此,初步研究后认为,沉积物粒度在水合物形成过程中扮演了重要角色,天然气水合物可能偏向形成于粒度大于31μm的粗粒沉积物中。更多还原

【Abstract】 A total of 614 sediment samples at an interval of about 1.5 m from all 5 sites of the Integrated Ocean Drilling Program (IODP) Expedition 311 on Cascadia Margin, northwestern Pacific were analyzed using a Beckman Coulter LS-230 Particle Analyzer. The grain-size data were then plotted against depth and compared with other potential proxies of gas hydrate-occurrence such as soupy/mousse-like fabrics in sedimentary textures, gas hydrate concentration (Sh) derived from LWD data using Archie’s relation, IR core images (infrared image) and the recovered samples of gas hydrate-bearing sediments. A good relationship was found between the distribution of coarse grains (sizes 31~63 μm and 63~125 μm) and the potential occurrence of gas hydrate across the entire gas hydrate stability zone (see the yellow zones in following 5 diagrams). For example, the depth distribution of grain size from the Site U1326 shows clear excursions at depths of 5~8, 21~26, 50~123, 132~140, 167~180, 195~206 and 220~240 mbsf. They coincide with the potential occurrence of gas hydrate indicated by soupy/mousse-like structures, logging-derived gas hydrate concentrations (Sh) and the recovered samples of the gas hydrate bearing sand layers. Therefore, sediment-size may have played a role in the concentration of gas hydrate. Gas hydrate occurs preferentially in relatively coarse-grained sediments (>31 μm in grain size).更多还原