Tahan-chi River flows through the southern part of the Taoyuan Prefecture located on the south of Taipei City, and Shihmen Dam, which is the largest water reservoir in Taiwan, is located there. Pliocene strata of the Kueichulin Formation and the Chinshui Shale, and Pleistocene strata of the Cholan and Yangmei formations are exposed about four kilometer long on the downstream side of the reservoir. The succession was basically formed by a transgression and a regression in the foreland basin of Taiwan Collision Zone. The upper part suggests upward swallowing from shelf condition to barrier island and river systems. However, we can find several small cycles of transgression and regression in this succession.

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This study presents that the grain-size distribution obtained by the hydrometer method is affected by diatom frustules in bulk sediments finer than 6 phi in median size. This fact implies that detrital grains need to be extracted from bulk muddy sediments to clarify sedimentary processes of detrital particles. This paper reveals that detrital grain size distribution of the surface sediments and sedimentary processes in Lake Kizaki, central Japan. Detrital grains were extracted by removing diatom frustules composed of amorphous opal, and were measured by laser grain size analyzer. Surface sediments can be divided into four groups. The Group I and II sediments are classified into clayey silt, and distribute in the offshore zone. The Group III sediments are of sandy silt or sand-silt-clay, and form transitional zone between the offshore and following nearshore. The Group IV sediments are of silty sand or sand, and their distributions almost correspond to nearshore zone. Boundaries between the Group III and Group IV cross the counter line toward offshore at the river mouth, implying that flood event plays an important role of sedimentation in Lake Kizaki. Sandy and gravelly sediments of the nearshore zone can be regarded as residual sediments by wave action. Sediments composed of transitional zone transported by waves and spread from the river mouth during flooding event and normal periods transported toward offshore, and then settle down quickly according to Stokes’ law. Moreover, fine sediments composed of the offshore zone remained suspended and appeared to be controlled by surface current.

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The Miocene Sekibutsu Tuff Member in Nara, southwestern Japan, is well preserved with resedimentation of volocaniclastic sediments of the Muro Ignimbrite. Reworked volocaniclastic deposits in the Sekibutsu Tuff Member is subdivided into three units, Unit A, B and C, in ascending order. Unit A is mainly comprised with debris-flow and hyperconcentrated-flow deposits, which buried eroding channel on the pyroclastic-flow deposits. Unit B consists of a massive to laminated tuff considered deposited from suspension in the standing water. Unit C is coarsening- and thickening-upward successions of interbedded debris-flow and streamflow deposits. These facies changes were represented in collapsing, erosion and resedimentation in the marginal distribution of the pyroclastic-flow deposits.

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