Flow property of the head of a gravity current formed by sediment suspension is investigated using the two-layered model. The theory takes account of pick up and deposition of particles as well as entrainment of the ambient fluid. Basic equations, those of conservations of volume and buoyancy and equation of motion, are developed by means of the characteristic curve method. Pick up rate of the particles is investigated using the experimental data. Numerical calculation shows that (1) when F₀ (F₀ is initial value of densimetric Froude number) is large and τ_*0/τ_*c(τ_*0 and τ_*c are dimensionless tractive force and its critical value, respectively) is smaller than unity, gravity current loses its velocity and density gradually but that (2) when F₀ is small and τ_*0/τ_*c is larger than unity, pick up always occurs and then gravity current increases its velocity and density rapidly. A diagram describing the division of these regions is obtained on the F₀-τ_*0/τ_*c plane.

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Measurement of the vertical distribution of total suspended matter (TSM) was carried out during summer throughout the Seto Inland Sea. TSM concentration near the bottom is influenced significantly by water movement and turbid bottom water is observed in all areas where median grain size (Mdφ) of the bottom sediment is more than 4φ. The high concentration of TSM near the bottom may be due to resuspension of the surface layer of bottom sediments.
We designed the special apparatus to measure the settling velocity of suspended particles in the sea. By using the apparatus, in situ measurements were carried out in Harima-Nada of the Seto Inland Sea. The settling velocity of the particles ranges from 8×10^-3 cm s^-1 to 2×10^-1 cm s^-1 and increases with particle diameter. The apparent density of the particles ranges from 1.38 to 1.03 and decreases with increasing particle diameter.

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In the oceans of the low latitude, the surface water mass of high temperature and low density is contacted occasionally with the deeper water mass of low temperature and high density. For the particles of sedimentary origin settling in the water column of this situation, the settling velocity would be decreased sharply at the contact due to the sharp increases of density and viscosity. If the sedimentary particles are supplied into the water column continuously, they may be crowded at this horizon due to the sharp decrease of settling velocity, or they can be advected with some kinds of vortices which may occur at the contact. The mechanism was analyzed and the water masses of this situation was investigated in the oceans surrounding the Ryukyu Islands. The contacts of such water masses are well developed in the water columns at the passage region of the Kuroshio and the settling behaviors of sedimentary particles should be studied at this region in the future.

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Basic patterns of the fine grained sediments on the C-M diagram, in which C is the one-percentile, M the median of the grain-size distribution, are summarized as pelagic suspension (quiet water deposits) and uniform suspension by PASSEGA (1957, 1964) and PASSEGA et al. (1969). However, the former is, as he mensioned in his '69's paper, based on a little data of the fine grained sediments. The course from uniform suspension to pelagic suspension on the C-M diagram has not been clarified.
To reveal the grain size image of the fine grained sediments, the fine grained sediments in the various sedimentary environments were analyzed using the same method with high accuracy, sieving method for the coarser part than 4.5phi and hydrometer method for the rest. Deposits of various environments are lacustline (Lake Kasumigaura), bay-estuarine (Tokyo Bay, Holocene marine deposits in the Lake Kasumigaura region, Lake Hamana), open type bay-inner shelf (Ishikari Bay, Sendai Bay), slope-basin (offing of Shimokita Pen., offing of Shioyazaki) and pelagic (Penrhyn Basin etc.).
It is revealed that:
1) Patterns of these data on the C-M diagram do not agree with pelagic suspension pattern of PASSEGA et al. (1969) and are like patterns of his basic data.
2) Among deposits of various enviornments in the minimum values of the median grain size and the maximum grain size, the following relationship are recognized.
M: pelagic (red clay)<lacustline≤bay, estuarine<hemipelagic (slope, basin)<inner shelf, open type bay
C: pelagic (red clay)<lacustline≤bay, estuarine<hemipelagic (slope, basin), inner shelf, open type bay
3) Changes in maximum grain size accompanied with decreasing the median grain size are like among these deposits except for Holocene marine deposits in the Lake Kasumigaura region, so these changes are considered to be the grain size properties of suspended deposits.
4) Deposits of various environments has almost no distributions in the area (C>4phi, M<8phi) on the C-M diagram.
5) Holocene marine deposits in the Lake Kasumigaura region has distributions close to the C=M line from 4 to 8phi in the median grain size as compared with the others and the narrow scattering in the C values, so are considered to be deposited under the constant flowing conditions.
6) Based on the data of turbidites previously reported, turbidites has nearer petterns to the C=M line than suspended deposits and distrubutions in the area (C>4phi, M<8phi) on the C-M diagram.

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The results of collecting piston core data and seismic profiling reveal the distribution of calcareous biogenic turbidites in the Central Pacific Basin. These turbidites originate on the Manihiki Plateau, the Line Islands Ridge, and the Magellan Rise. The sedimentation of turbidites originating on the Magellan Rise and the northern Line Islands Ridge had ceased since the Miocene, out of the high organic productivity zone around the Equator. But the Manihiki Plateau and the southern Line Islands Ridge have been supplying calcareous biogenic turbidites to the eastern Central Pacific Basin.

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The characteristics of grain size distributions of muddy surface sediments off southwest Japan are discussed. The results presented in this article are based on 300 textural analyses and 133 clay mineral analyses.
Muddy sediments are distributed on the continental shelf and continental slope-deep sea terraces. Judging from the characteristics of grain size distributions and compositions of clay minerals, muddy sediments on the continental shelf are distinguished from those on the continental slope-deep sea terraces. The grain size distributions of surface sediments of the deep sea terraces slightly differ from those of the turbidites.

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Jurassic mudstones with cerium positive anomalies are found in the Tamba Belt, Southwest Japan. One of them is a dark green radioralian mudstone with manganese oxide. Another is a reddish brown fine-grained mudstone which is enriched in iron oxide and contains 2 or 3 percents of radioralian tests, quartz and feldspar.
The former shows Ce positive anomaly which is closely correlated to the enrichment of rare earth elements in deep sea manganese nodules. In the latter case, selective accumulation of manganese is not found. So that, rare earth elements, especially cerium, are incorporated in deep sea sediment with authigenic minerals and/or adsorption under oxic condition.
Above mentioned mudstones are both considered to be ancient oceanic sediments. In future, other sediments of the same origin will be found among the sedimentary rocks of the “Honshu Geosyncline”.

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Preliminary chemical analyses of authigenic chlorite, glauconite, illite and koalinite in two argillaceous rocks from Paleogene Ishikari Group using energy-dispersive type microprobe give fairly well cationic total and structural formulae of these minerals. The amounts of expandable layer in mixed-layer mineral estimated from the chemical composition are close to those estimated from the X-ray diffraction of clay fractions. Chemical composition of illites are clearly different from that of coarse-grained, detrital white micas. The results show the validity of microanalyses of fine-grained sheet silicates in sedimentary rocks. The limitation of quantitative microanalyses in argillaceous rocks is also discussed.

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Shallow marine deposits of the Koguchi Member of the Early to Middle Miocene Kumano Group in southeastern Kii Peninsula consist of muddy sediments with varying proportions of coarser interbeds. The coarser interbeds which are made up of fine-grained sandstone and siltstone are interpreted as storm deposits, judging from the following sedimentary features. 1. Thin beds of sandstone and siltstone alternate with layers of generally bioturbated mudstone. 2. The beds of sandstones range in thickness from 1 to 15cm and exhibit marked evenly parallel lamination, and crude normal graded bedding, and have carbonaceous laminae at times. 3. The beds of sandstone and siltstone have a sharp lower contact and grade upward into mudstone, and have trails of organisms and sole marks such as flute cast and load cast on soles of beds, and burrows oblique to the bedding plane in beds. 4. The discontinuous low-angle cross lamination, ripple lamination, ripple-drift cross lamination and hummocky cross stratification (HARMS et al., 1975) are observed above the parallel lamination in beds. 5. Some sandstone beds show internal structures of graded rhythmite (REINECK and SINGH, 1972). 6. The alternating beds of sandstones and mudstone occurs in horizon between the offshore mudstone facies (Shikiya Member) and the shoreline facies (Miyai coal-bearing Member). 7. Sandstones are almost feldspathic (to quartzose) arenite and maturer mineralogically and texturally than those of turbidite facies association with a large amount of matrix, composite quartz and lithic rock fragments.
On the viewpoints of mineralogical and textural maturity, it is possible to distinguish between storm sandstone and turbidite.

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“Inverse grading” structure characterized by upward-coasening sequence is known to be well developed in flood deposits of meandering sand-bed rivers in Japan. This structure consists of two layers, the lower mud and upper sand, formed during a single flood. The depositional process was already elucidated.
The flood deposits on floodplain are composed of the alternation of sand and mud with many “inverse grading” structures. They are commonly recognized in following three subenvironments, slipoff slope, natural levee and backswamp. The deposits of each subenvironment contains many intercalated sand layers with characteristic sedimentary structures.
Many “inverse grading” structures are found out from the Late Pleistocene fluvial deposits in the Tsukuba Upland, Ibaraki Prefecture. We can easily dicide the subenvironments of flood deposits from the strata by means of the “inverse grading” structure.
The “inverse grading” structure is a distinctive indicator of flood deposits in meandering system.

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Comparison of grain size in the fields of geology, pedology, and soil engineering was made on viewpoints of 1) classification and names of each grain size, 2) mechanical grain analysis, and 3) method of each expression of the results of 2).
These are quite different system in each field as are shown in Fig. 1. And therefore, much discussions and adjustments among them may be needed, even if each field has each own object.

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