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 (S_h) 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 (S_h) 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).