1989年夏の日本海におけるODP Leg 127/128航海で3地点において中新世砂岩が採取された. 船上観察によれば, こららの砂岩は中～上部半深海で混濁流によって堆積したものと思われる. これら砂岩の岩石学的・地球化学的研究によると, 日本海盆東北部第796地点の後期中新世砂岩は北海道南西部またはその近傍の未開析火山弧中の火山砕屑性源岩から由来した. 大和海盆中の第797地点の初期中新世砂岩もまた主として火山源であった. この源岩地域は中部本州西方の, 幾らか変成岩, 堆積岩, 深成岩, なども含む未開析ないしそれに近い火山弧に位置していた. 北大和トラフの南西端に位置する第799地点の初期中新世砂岩の源岩は主に花こう岩質岩で, 若干の火山岩, 変成岩, 堆積岩を含むものであった. 第799地点砂岩の主要供給岩は, 北大和堆の花こう岩質岩であったと思われる.

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Bottom water movements on the outer shelf and marignal terrace off San'in district in the southern Japan Sea are discussed based on sedimentological data such as sediment distribution, distribution and morphology of bedforms, sediment composition and seismic records. Sediment transport and deposition is highly controlled by water circulation in this area. Transport of sandy sediments, and sea bottom erosion and/or non-deposition of modern sediments occurs. Directions of sediment transport judging from sedimentological data are from west to east. This is the same as those of the second branch of the Tsushima Current which flows just over this area and of the eddies which formed between the branches of the Tsushima Current. Beneath the first branch and/or between the first and second branches, modern muddy sediments were distributed. One of them is thought to be deposited in the eddies between the first and second branches at the east of Oki Islands. Bottom currents are also considered to be influenced to the distoribution on the basis of the disturbbution of biotite and volcanic glass shards which have been reworked and transported by the bottom currents at the east of Oki Islands. On the other hand, a small submarine canyon, in which modern sediments have not been deposited and the older sediments are exposed, is located on the mariginal terrace off Tottori. These sedimentological facts indicate the presence of bottom currents along the canyon aixs.

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The Izumi Group developed in the western part of the Asan Mountain Range is composed of normal marine deposits (Kaino Mud Stone) and turbidity deposits (Takikubo Alternation of Sand and Mud). In this study, the authors tried to distinguished those two deposits by finding the orientation of the longest axis of the imbricated gravels and sands in the sandstone. In a consequence of the measurements, the boundary of those strata become clearly, and the debris which made up the Kaino Mud Stone, normal marine deposits, were mainly from the NNW region. Likewise debris forming the Takikubo Alternation were brought from the east of the area by the turbidity currents.

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The Hakubuchi Group is the uppermost unit of the Yezo Supergroup, a forearc basin sediment distributed along the meridional zone of Hokkaido, Japan. The group in the Sorachi Anticline represents the western marginal facies of the basin, showing conspicuous lateral facies changes. It is subdivided into three formations, Hk₁, Hk₂ and Hk₃, based on the facies distribution. The upward shallowing succession of Hk₁ and Hk₂ in the eastern limb of the anticline, which is composed of inner shelf to delta plain facies through shoreface, foreshore and beach facies, is interpreted to be a lowstand delta on a conformable sequence boundary. The massive conglomerate facies constituting very thick Hk₂ in the western limb and only the uppermost of Hk₂ in the eastern limb, may be a transgressive systems tract. The base of the conglomerate in the wester limb corresponds to an erosional sequence boundary. A highstand systems tract is represented by Hk₃ distributed widely in both limbs. The upper two parasequences of the three recognized in Hk₃ had been partly eroded away under a sequence boundary (clinounconformity) with the Eocene coal measures, Ishikari Group. Therefore, the Hakobuchi Group constitutes a depositional sequence during 10m.y. (Lower Camapanian-Lower Maastrichtian).

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Fabric and structure in clast-supported fluvial conglomerates of the Oligocene Noda Group display channel floors of rather high-sinuosity. A key structure of such channel deposits is a symmetrical or asymmetrical concave-up gravel alignment. Dip angle of some gravels is very high. Such high-angle dip direction was probably the product of resultant force of the gravity pull and the traction current that imbricates the gravels to the upstream dip.

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The Middle Miocene Katsumoto Formation, distributed in the northern and central part of Iki Island, Nagasaki Prefecture, has been considered as a typical back-arc basin sequence. This study aims to describe sedimentary facies, ichinofacies and paleocurrent system and to discuss sedimentary environments and depositional systems. The Katsumoto Formation, attaining more than 450m in thickness, shows a coarsening- and thickening-upward sequence as a whole. It begins with mud-dominated facies of interbedded sandstone and mudstone, passes upward into medium-bedded, medium-grained sandstone and siltstone facies, and ends with thick-bedded, medium- to coarse-grained sandstone facies at top. Six sedimentary facies recognized. Their lithologies are summarized as follows; Facies A: mainly well-sorted, medium to very coarse sandstone with planer to tabular cross-stratification, Facies B: well-sorted, very fine to medium sandstone with amalgamated hummocky cross-stratification (HCS), Facies Ca: interbedded HCS sandstone and siltstone, Facies Cb: thinly interbedded HCS sandstone and siltstone, Facies D: mottled sandy siltstone with thin very fine-grained sandstone, Facies Fa: slump breccia, Facies Fb: slump folded thinly interbedded sandstone and mudstone, and Facies F: interbedded very fine-grained turbidite sandstone and mudstone. The sedimentary environments inferred from Facies A to F are summarized as follows; Facies A: upper shoreface, Facies B: lower shoreface, Facies Ca and Cb: inner shelf, Facies D: outer shelf, Facies Ea: shelf margin, Facies Eb: continental slope, and Facies F: basin plain. Fossil evidence, such as burrowing organisms and benthonic foraminiferas obtained from the formation, seems to coincide with these environments. Eastward and northeastward paleoflows are dominant in the lower, and the middle and upper parts of the formation, respectively. It can be concluded, therefore, that the Katsumoto Formation represents a facies succession from basin plain to tide-dominated shallow marine sediments due to northeastward progradation process. The northeastward progradation system is also recognized in the regional area of the Tsushima Basin in the Middle Miocene time.

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At least ten cyclic changes in sedimentary facies and accompanying molluscan fossils can be recognized in the middle part of the Omma Formation in Central Japan. The middle part of the Omma Formation is dated as early Pleistocene (1.3-0.9Ma) which is a period that is known to have experienced major fluctuations in sea-level and climate caused by glacio-eustacy. Glacioeustacy can therefore be selected as a strong candidate for explaining the observed cyclic changes in both lithofacies and molluscan fossils. In order to test the validity of this interpretation, we compared the water-depth curve inferred from molluscan fossils in the middle part of the Omma Formation with the oxygen isotope record of DSDP Site 607. The bottom and top of the Jaramillo Subchron (the most precise datum horizons) and three nannofossil biohorizons can be used to give very good time constraint. The results show that the pattern of changes in water depth recorded by the fossil and sedimentary records exactly coincides with the oxygen isotope record at Site 607. The close match between the two records lead to the following conclusions:
1) the depositional age of the middle part of the Omma Formation corresponds to the oxygen isotope stages from 46 to 28; and
2) the observed cyclic changes in sedimentary facies and molluscan fossils can be best explained as the result of glacio-eustacy with a period of the 41, 000-years, which corresponds to the period of orbital obliquity of the earth.

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The Middle Pleistocene (0.5-0.7Ma) Saijo Formation consists of braided river- and meandering river siliciclastic deposits, 30-50m thick, developed in three basins, Hokubu-Saijo Basin (NSB), Nambu-Saijo Basin (SSB) and Kurose Basin (KB) from the northeast to the southwest, in the central-south Chugoku region. The braided river deposits represented by thick-bedded sand-sandy gravel facies mainly occur in NSB, whereas the meandering river deposits are developed throughout both SSB and KB, which are characterized by marked fluvial cyclic depositional facies. The cyclic facies comprises four depositional unit types, types I-IV, with varying thickness, showing different environments from of high energy to low energy. Analysis of the distribution pattern of the each facies, combined with paleo-current data, suggest that the Saijo Formation was formed in a serial fluvial system comprising upper stream area of NSB to lower one of KB via intermediately situated SSB. Development of the cyclic depositional facies in SSB and KB suggests that a frequent migration of channels and floodplains occurred in the meandering river. The Saijo fluvial depositional basins are suspected to have formed affected by left-lateral faulting under marked E-W regional stress-field, and E-W flexural uplift of SSB relative to KB after the deposition may have been related to regional upheaval of the Chugoku region, although relevant tectonic aspect is still open together with detailed depositional processes of the Saijo Formation.

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The Plio-Pleistocene Osaka Group is developed in the central part of the Kinki District. The group consists of nonindurated gravel, sand, silt and clay beds, deposited in fluvial, lacustrine and shallow-marine environments, and includes, also, more than 45 volacanic ash beds. The author carried out a detail study of the succession just above and below the Fukuda volcanic ash layer, in the southern part of Kishiwada City, Osaka Prefecture, for reconstruction of sedimentary environments.
Within an area of 6×1km², ten sedimentary facies were distinguished. These facies can be grouped into five facies associations, according to the coexistence of sedimentary facies. According to succession of facies associations and lithostratigaphy, the Osaka Group in the study area consists of sediments of two sedimentary environments: river channel and bars of intermediate to low sinuosity and high braiding parameter, and flood plane with the ephemeral channel of low sinuosity and high braiding parameter.

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The Plio-Pleistocene Osaka Group distributed in Fukakusa, at the eastern part of the Kyoto basin, can be divide into four depositional facies. They are (1) fluvial channel gravelly sand with tabular and trough cross-stratifications, (2) inter-channel or abandoned channel sand and mud with inverse grading and rootlets, (3) massive gravel and ill-sorted gravelly mud of debris flow origin, and (4) bay floor mud with plant debris and burrows. The mud beds of (4), so called “marine clay beds” are repeatedly interbedded between fluvial deposits of (1) to (3). The fluvial deposits of (1) to (3) are in braided river system developed at the lowstand of sea-level, and in contrary the marine mud of (4) was deposited at the highstand during glacio-eustatic changes.

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Grain-size analysis of muddy sand or sandy mud is a matter of trouble, because the sediments abundantly include both sand and clay grain size which behave differently in principle. The analysis by a single method needs a very long time and/or a large labor for one specimen.
The new procedure proposed here is a combination of a settling tube method for sandy fractions and a hydrometer method for muddy fractions. The hydrometer analysis is performed according to an ordinary procedure. Then wash the sample on a 4.5-phi standard sieve. Dry the fractions rested on the sieve, and weigh it. After then, analyze the coarse fractions by a settling tube method. The settling tube method is a newly-formed system which uses an electric balance and a computer. Make the two cumulative frequency curves, and combine them by calculation. Theoretically, both curves should fit at 4.0 phi of settling-size grade, on the basis of the detailed research of effects by 4.5-phi sieving. Both curves, however, often differ slightly at 4.0 phi. Therefore, they are shifted to each other at 4.0-phi grade by changing the total weight of the used sample, namely “weight correction”. This procedure takes 4 days to analyze 15 samples from coarse-grained sand to clay.

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Combined-flow ripples were produced in a recirculating flume with wave-generator at the Osaka University. Waves propagate against the current direction in the flume. The combined-flow ripples in our flume show the characteristic profiles of rounded lee and stoss sides and rounded troughs. The roundness of ripple profiles decreases by the incresing of oscillatory velocity, and the symmetry changes weaker related to the increasing of unidirectional velocity. Ancient combined-flow ripples, which have been recognized as wave ripples, are also introduced from the shallow-marine stratigraphic record.

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