Clay minerals in a long sediment core collected from the Danjo Basin off Nagasaki Pre. Japan were studied by XRD & ATEM. The presence of illite, chlorite, smectite, and kaolinite were clarified by XRD. Illite is the most predominant clay mineral while kaolinite shows the lowest concentration of the four clay minerals assemblage. The clay mineral composition in this core samples is similar to that of the East China Sea. The clay minerals contained in the uppermost part, middle part and the lowest part layers of the sediment core were investigated by ATEM. Chemical characteristics of each clay mineral are precisely and quickly determined by this method. Results obtained may play an important role in the development of sedimentology as well as clay mineralogy.

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The Surface sediment types in the North Pacific region are characterized by grayish mud in the hemipelagic marginal area of the continent, red clay in the pelagic deep sea, and calcareous ooze on the seamounts shallower than calcite- compensation depth (CCD). While the hemipelagic gray clay is covered by thin (less than 10m) oxidized brown clay on its surface, the red clay in the pelagic seafloor is usually several tens of meters thick and underlain by bedded chert in the North Pacific. Thickness and stratigraphy of the pelagic (red) clay and bedded chert were compiled from the lithologic descriptions of the Deep Sea Drilling Project (DSDP) cores in the North Pacific region.
As a general scheme in the North Pacific, several tens of meters of pelagic clay are underlain by the Eocene to Cretaceous interbedded unit of bedded chert and pelagic clay of less than 100m, the Cretaceous chalk with occasional occurrence of flint nodules, and the basement basalt in the descending succession. The thickness of the pelagic clay is thinnest at the peripheral area of the East Pacific Rise, and the pelagic clay is overlain by thick gray clay at the hemipelagic margin, as possible results of the subduction of pelagic clay beneath hemipelagic gray clay. The thickness of the interbedded sequences of bedded chert and pelagic clay does not vary at the wide areas of the North Pacific; however, the geographical distributions of the Eocene-Cretaceous unit of bedded chert-pelagic clay interbeds and the Cretaceous unit are restricted as belts and change older in a northwestern direction from the equatorial belt. A schematic cross section of these deep-sea stratigraphic units across the Northwest Pacific may demonstrate lateral and vertical facies changes due to the lateral spreading of the Pacific plate in ages.

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Grain size distributions of about 500 samples of marine sediments off Northeast Japan and in Central Pacific Ocean were measured using the fixed method with high accuracy, a sieving method for the coarser part than 4.5 phi and a hydrometer method for the rest.
These fine-grained sediments have common three characteristics in the finer part than about 3 phi in median diameter. These are positive skewness, poorly sorting and the decrease in skewness in keeping with fining of the grain size. Among the marine sediments, decrease in silt content, illness of the sorting and fining of the finest median grain size are recognized with an increase in the distance from the land. Most of the turbidite mulls are well sorted between 3 to 6 phi in median diameter in comparison with the other fine-grained sediments.

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