The history of sedimentology in Japan has briefly been reviewed. The word ‘taisekigaku’ for ‘sedimentology’ was introduced into Japanese scientific terms as early as 1950, much earlier than in the international community. The development of sedimentological researches in Japan is divisible into three stages; the first (1950s), second (1960s-1970s) and third (1980s-). The Sedimentological Research Group established in 1957 was reformed three times in 1968, 1971 and 1991. The present Sedimentological Society of Japan (about 550 members) started with the renewed biannual journal “Journal of the Sedimentological Society of Japan” in 1991.
For future development of sedimentology in Japan, the following suggestions have been made; (1) keep away from the Renaissance-style of researches, (2) contribute to the environmental sedimentology, and (3) globalize research activities. For this purpose the organization of regional meetings in Asia is suggested under the auspices of IAS.

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The distributary-channel deposits of the Tertiary Taishu delta system record the interaction of tidal and fluvial processes. Mud-draped cross-stratification and flaser to lenticular bedding are common in the distributary-channel deposits, indicating intermittent migration of bedforms governed by tidal processes. In spite of the clear evidences of tidal influences on distributary-channel sedimentation, paleocurrents of channel deposits are not multi- or bidirectional but are consistently unidirectional. The bundles of mud-draped foresets also do not show the neap-spring tidal cycles as represented by a regular change in the bundle thickness. In the distributary channels, tidal processes should have superimposed on fluvial processes. The combined effect of fluvial and ebb-tidal flows acceralated down-channel migration of bedform, whereas the effect of flood tide was probably set off by fluvial flows not to produce reversal currents within the channel. Fluctuations in fluvial discharge prevented the regular tidal cycles to be recorded in the channel deposits.

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Sequence stratigraphy of the Upper Pliocene to Lower Pleistocene in the Niigata Basin was established by reviewing and correlating among previous sequence stratigraphic studies, in order to clarify the characteristics of depositional systems in a tectonically active basin. The Upper Pliocene to Lower Pleistocene strata (3.6Ma-1.1Ma) in the Niigata Basin are divided into “Sequence Ngt. III. 1. N1”, “Sequence Ngt. III. 1. N2” and “Third order sequence Ngt. III. 2” in ascending order.
“Sequence Ngt. III. 1. N1 and Ngt. III. 1. N2”, which correspond to No. 3 Globorotalia inflata bed, mainly comprise slope-submarine fan turbidite-trough-fill turbidite systems. On the other hand, “Third order sequence Ngt. III. 2”, which corresponds to the horizon ranging from tephra key bed “Hap-2” at the base to “SK030” at the top, mainly comprises shelf-nearshore-delta-fluvial-alluvial fan systems in the southern part of the basin. These paralic to terrestrial depositional systems show a large scale progradational pattern from the southern part of the basin toward the north through the third order sequence, although a small scale retrogradational or aggradational pattern is observed in TST. In addition, “Third order sequence Ngt. III. 2” contains high frequency depositional sequences, which were formed in response to glacio-eustatic sea-level changes.

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The eastward progradation of the barrier shoal deposits in the highstand systems tract (HST) of the Arab-Hith depositional sequence was controlled by the third-order sea-level change which constructed the vertical stacking pattern of HST in the GA Field. The stratal pattern of HST in this depositional sequence reveals progradational/aggradational. This stratal pattern is similar to the lapping pattern in highstand systems tract of the Exxon model.

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Surface unconsolidated carbonates were sampled from lagoonal basins in the Shiraho and Sekisei Coral Reef areas, the Yaeyama Islands. Lime mud fractions were isolated from these carbonates by sieving and sedimentation methods to collect particles between 62.5μ and 2μ. The isolated lime mud fractions were analyzed for carbonate-bound trace elements, CO₃ contents, mineralogical compositions by the X-ray diffraction analysis (XRD), and petrographic observations including scanning electron microscope (SEM) observations. The carbonatebound trace element concentrations were determined by subtracting the 0.75 N LiCl-0.25N CsCl in 60% ethanol leachable fraction from the 1N ammonium acetate-acetic acid (pH adjusted to 5.2) leachable fraction. Lime mud is composed mineralogically by HMC (high-Mg calcite), HSA (high-Sr aragonite), LSA (low-Sr aragonite), and LMC (low-Mg calcite). However, the carbonate-bound Mg/Ca and Sr/Ca ratios are considerably lower in lime mud than the carbonate sand and gravels which contain the same amount of carbonate minerals with the lime mud. This suggests that Mg and Sr were leached without changing mineralogy during the formation of lime mud from coarse carbonate grains. Diagenetic changes in lime mud might have already started before its lithification processes to limestone.

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Extensive occurrence of iron silicate oolites have been observed in the Upper Pleistocene subsurface sediments of Mahanadi delta along Orissa coast. They are usually associated with dark grey to black, shell-bearing marine deposits now occuring inland at depths ranging from 100 to 300m beneath the present ground level. They show concentric layering with or without a nucleus and are believed to have been formed by the precipitation in amorphous state of hydrous iron silicates of variable composition approximating between glauconite and chamosite. They were deposited in a shallow marine reducing environment.

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The main purpose of this study is to clarify the relation between characteristics of sediments and environmental conditions, based on the analysis of core samples from the South Yatsushiro Kai (Sea) which is located off the west coast of central Kyushu Island, Japan.
Bottom sediment samples were collected at 74 stations in the southern part of the Yatsushiro Kai using gravity corers in March 1996. 62 core samples were used for the mechanical analysis by the settling-tube method, and Q-mode cluster analysis was carried out based on the proportion of grain size distribution (Wentworth size classes). 61 core samples were available to estimate the sedimentation rates (during c. 50 years) which were recognized from the first appearance of high mercury contents of cores. On the other hand, the topmost one centimeter of 73 core samples, which is approximately 10cc of wet sediments, was utilized for foraminiferal study.
The general trend of the bottom current system in the area was discussed, based on the mechanical analysis data of bottom sediments, the distribution of sedimentation rates and the distributions of the number of individuals of planktic and living benthic foraminifera. Based on the results mentioned above, the South Yatsushiro Kai is subdivided into the following five areas: 1) the area near the straits characterized by coarse sediments under the influence of strong tidal and bottom currents; 2) the southern part and the area off the mouth of the Minamata River, both of which are characterized by relatively coarse sediments under the influence of longshore currents and poorly sorted sediments supplied by the Komenotsu and Minamata Rivers; 3) the northwestern and eastern parts characterized by fine-grained sediments accumulated under conditions of rather stagnant water masses; 4) the central area, characterized by relatively fine sediments and a large number of planktic empty tests deposited on the sea bottom under the condition of rather weak tidal current systems; 5) the northern part characterized by gravels or gravelly sands which were derived from shallow coastal areas.
Judging from the distribution pattern of the maximum mercury content at some horizons of each core, the fine-grained sediments polluted by mercury were transported northeastward and southward by weak longshore currents and spread toward north and west across the northern and southern parts of the South Yatsushiro Kai.

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Two-different point-counting methods of thin-sectioned sands have been argued in evaluating their grain size effects and aims. The traditional method that reflects the dependence of modal composition on grain-size quite differs from the Gazzi-Dickinson method that shows the total independence of grain-size in thin-section analyses. Sets of goals by the two methods do not seem to be the same; the traditional method aims to demonstrate the effect of depositional environments, climates and diagenesis of sediments, whereas the primary target of the Gazzi-Dickinson method is mainly to clarify tectonic settings in provenances.
In an attempt to avoid some confusions raised by the two different point-counting methods, we reveal that there will be no significant difference of petrographic data between two methods if we restrict the sand or sandstone samples less than 2.0phi of mean diameter.

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