Mud flat sediments in the Ariake Sea (Bay) are widely distributed at the western area of the inner part, and sandy tidal flat sediments are developing along the coast of the outer part in Kumamoto Prefecture. At Toguchiura beach, the Uto Peninsula, we can recognize seventeen intertidal sandbars. Their ridges are sinuous in plan and subparallel to the beach. Many wave ripples are constructed on the intertidal sandbars by waves in the wind during high tide. The crest line of wave ripples is oblique to the ridge of these sand bars. The peaked crests of wave ripples on a seaward slope of these bars are eroded with weak wave action just before subaerial emergence of wave ripples, and become rounded or flattened. Wave ripples on a landward slope are very little deformed by waves because of the shadow of the ridges. As the result, the attitude of wave ripples is characteristics at the position on intertidal sandbars. Their difference is very important as a criterion for discriminating the seaward direction of the intertidal sandbar.

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Three kinds of bedforms, such as large and medium subaqueous dunes and ripple marks, are observed in the Oki Strait, located between the Shimane Peninsula and the Oki Islands, southern Japan Sea. As surface sediments in and around the Oki Strait become finer eastward and profiles of large subaqueous dunes show the asymmetrical forms with steeper eastern slopes, the direction of sediment transport is eastward. No evidence which shows westward sediment trasnport at the western past of the Strait indicates that bedforms found in the Oki Strait were formed by unidirectional current such as ocean current rather than by bidirectional tidal current. Bedform arrangement lacks rippled sand sheet in the typical one which is formed under modern hydraulic conditions. The occurrence of large subaqueous dunes with indistinct crest forms and eroded by medium subaqueous dunes, and of medium subaqueous dunes destroyed its crests by the fishery activities and the lack of rippled sand sheet indicates that the bedform system in the Oki Strait is abandoned one. It may be formed during the transgression after the last glacial age.

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3.5kHz SBP (サブボトムプロファイラー) 記録の分類と空間的分布の解析及びコア試・資料の観察により, 熊野舟状海盆における堆積相と堆積作用の解明が試みられた. 本舟状海盆底には, 南西側と南東側に海底扇状地状堆積体が存在する. 南西側のそれは現在も活発な堆積作用が継続しており, コア試料には, 厚さ1cmから数10cmの細粒～極細粒タービダイト砂層が半遠洋性泥層の中に多数狭まれている. 一方南東側のそれは, アカホヤ火山灰層 (約6300年前) より下にのみ, 極細粒砂のタービダイト砂層が観察されることから, よりディスタルで, 現在の堆積作用は不活発である. いくつかの海底谷の頭が発達する中央の大陸斜面の中部では侵食作用が, 海底谷では堆積物の通過が, また海底谷の外側では半遠洋性細粒物の堆積作用が卓越している. 海底谷の出口付近には, 幾つかのタービダイト砂層がコア堆積物中に挟まれていることがある. しかしながら, 舟状海盆北側中央に位置し幾つかの海底谷を有するこの大陸斜面の麓には, デブリーフローの堆積体の存在は一部認められるが, 海底扇状地状堆積体は発達していない.

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The Obitsu River has built an arcuate delta extending 4km into Tokyo Bay, central Japan. The delta consists of top-set, fore-set slope and bottom-set morphology and the topset is divided into a subaerial and a subaqueous delta plain. The water depth of the boundary between the topset and the foreset slope is about 5m. The subaqueous delta plain is mostly composed of a tidal flat with a width of 1.2-2.3km and ranging from high tide level to a depth of about 3m. Well sorted and cross-laminated fine sands are distributed on the tidal flat and wave ripples are commonly recoginized from +0.6m to -2.8m in altitude. The direction of their crests is parallel to the shoreline in fairweather. Sand bars less than 50cm in height and 25-40m in wave length are distributed across 200-700m on the lower part of the tidal flat. The foreset slope is composed of mottled muddy sands with molluscan shell fragments. The maximun gradient of the slope reaches about 5° at the uppermost part of the slope. The bottomset consists of sandy mud to silt or shelly sands.
Fair-weather wavebase is estimated to be about 5m based on grain-size distribution and sedimentary structures of surface sediments and corresponds to the boundary between the topset and the foreset slope. In storm conditions, the topset sediments are eroded and transported such that sediments and molluscan shells are supplied to the foreset slope.

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Spatial and time-series distributions of nepheloid layers (layers of suspended sediment) were investigated in Kin Bay of the Okinawa Island, using light-scattering type nephelometers and moored observation stations equipped with current meters and other oceanographic recorders. Spatially, three types of nepheloid layers were observed in the bay: (1) frontal nepheloid layers at the estuary of the inflowing rivers; (2) bottom nepheloid layers formed by resuspension of bottom sediments; and (3) intermediate nepheloid layers in the thermoclinal intermediate water columns of the offshore waters. Cross profiles of temperature, salinity, and turbidity in the frontal nepheloid layers suggest that inflowing suspended reddish soils are depositing massively at the frontal estuary region. The formation of thermoclines was observed in rather offshore region where colder offshore deep waters may enter and mix with warmer coastal waters. The formation of thermoclines in the intermediate water colums was also seasonal and influenced the formation of intermediate nepheloid layers which may be formed due to the slowing of settling velocity of sinking particles.
The turbidity in the bay increases with the increased discharge of river waters which are also influenced by precipitation. The turbidity was increased by the tidal resuspension processes which occurred usually at the turning phase from high (flood) tide to low (ebb) tide.

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Clast fabric of trough cross-stratification as shown in Fig. 2 claims attention, suggesting depositional mechanism of the clasts of the Early Pleistocene fluvial sediments in Uji, Kyoto, Japan.

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The grain-size is one of the most important characters for the study of sedimentary environment of clastic sediments. It is impossible that the wide range grain-size analysis using small quantity grains with one method. Therefore the grains divided into sand size and silt size. The sand size grains are analyzed by the Emery tube, silt size grains are analyzed by the micron photo sizer. The process of this method is described in this paper. The advantages and problems of this method are discussed using the examples of turbidite sandstone, shallow marine sandstone and fluvial sand.

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A simple and practical method for estimating salinity is described in this paper based on pyrite (iron disulfide) content in carbonaceous materials by using a reflected microscope. The pyrite content is defined as the proportion of carbonaceous particles which contain pyrite in one hundred carbonaceous particles under microscope.
The presence of pyrite in organic sedimentary rocks has been considered to be a result of sulfate from sea water, iron from hinterland, and carbonaceous materials as a reductant in coal swamp.
Stratigraphic variations of pyrite content by this method were measured in four areas of Southwest Japan. The pyrite content in three Tertiary areas is in accordance with aquatic environments as previously reported. However, no correlation was observed between pyrtite content and estimated aquatic environments in the Omine coalfield where iron content varies considerably. This method will be employed as a useful tool to investigate sedimentary environments.

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Inverse grading of mud and sand is known in flood deposits in Japan (ISEYA, 1982), Many inversely graded beds are found out also in the Late Pleistocene fluvial deposits in Ibaraki Prefecture (MASUDA and ISEYA, 1985).
Recently we discovered inversely graded bed in the Lower Pleistocene alluvial fan sediments in the southern part of the Uji Hills. This inversely graded beds are intercalated in the upper part of the fining-upward sequence deposited on an abandoned fan lobe surface. This sequence is composed of gravels (facies A), trough cross-bedded sands (facies B), inversely graded beds (facies C), and bioturbated massive mud (facies D), in ascending order.
Facies C is deposited strongly affected by bed forms of facies B. It consists bioturbated thin alternations of mud and fine-grained sand, on the top of bars, whereas parallel-laminated medium-grained sands accumulate on the flat fluvial floor. Inversely graded beds develop thickest on the face of the bars inclining about 20-30 degrees and form laterally accreted depositional bodies.
Depositional sites of the inversely graded beds of the Lower Pleistocene Group can be better compared with slope and top of the bars of modern sandy low sinuosity rivers rather than flood plains. Bioturbated and vegetated marshland developed in the later stage, resulting from lateral accretional deposition of inversely graded beds.

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An aggradational sequence of lacustrine to marine deltas is developed in the Plio-Pleistocene Osaka Group, a standard succession in Japan. Each parasequence of prograding delta consisits of three facies, prodelta muds, delta-front alternation of sand and mud, and delta-plain braided river sands, from lower to upper. The parasequence bondaries are very sharp and there is few transgressive deposits above the boundaries. Moreover, debris flow deposits snd deformed beds with convolute structures, dehydration, and synsedimentary faults can be observed at the just under the boundaries. The environments, depositional facies, sequence, and tectonic setting of the deltaic sequence in the Osaka Group are very similar to the modern deltas of the Lake Biwa, where the delta aggradation have been controlled by active fault movement. From these facts and results, we may conclude that the cyclic repetation of the progradation of delta and the rapid rise of water level caused by the active fault movement associated with earthquake formed this aggradational deltaic sequence.

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The Izumi sedimentary basin (ISB), origined pull-aparts with strike -slip duplex structure, is developed at the Gojo releasing fault bend of the Median Tectonic Line. Izumi Mountains, Southwest Japan. Remarkable slump folds are found in the infilled Izumi Group (Upper-Cretaceous). On the basis of the tectonic analysis of the slump folds, the eastward slumping is considered to have been caused by tectonic tilting closely related to a rapid tectonic subsidence (ca. 1.7m/ka), obtained from the cumulative stratigraphic thickness versus F. T. ages of the Izumi Group.

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