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We analyzed grain-size distributions of a total of 275 sediment samples from unconsolidated Miocene horizons from three sites (135 samples at Site M0027, 80 samples at Site M0028, and 60 samples at Site M0029). Their horizons cover approximately the upper half of Sites M0027, M0028, and M0029, ranging 293, 177, and 164 m, respectively, a total interval of 634 m. Mean grain size of measured samples from three sites ranges from silt to coarse sand; however, it is differentiated to fine–medium silt and medium–coarse sand due to a limited occurrence of coarse silt to fine sand. Silty sediments dominate as a whole, and clay-dominated sediments were not recognized. Mean grain-size data plotted on the equivalent intervals of geologic columnar sections show several stratigraphic changes concordantly reflecting lithology and sequence stratigraphy at all three sites. Grain-size frequency curves of silty sediment samples measured by the laser scattering particle size distribution analyzer can be divided into 16 types on the basis of the mode shape and position, range of grain size, and volume of skewed coarser or finer grain components. Grain-size frequency curves of sandy sediments measured by particle analyzer with digital image processing can be also divided into 8 types. These types of grain-size frequency distributions also show several stratigraphic changes considerably concordant to lithology mean grain-size curves and sequence stratigraphy in general.