Facies analysis of sediments based on the boring database systems of the Osaka, Kyoto, and Kameoka basins situated in the central part of the Kinki district, Japan, have been carried out to correlate their subsurface sediments. The analytical method is the one which calculates the appearance percentage of clay, sand, and gravel at the same elevations and at 0.5m intervals in each of the basins, and then smooths these data using the moving average method for 21 terms. As a result, it has been revealed that the fluctuations in the appearance percentage of clay in the Osaka basin occur with a frequency very similar to the fluctuations of oxygen-isotope ratio in the upper part of core V28-239 raised from the Solomon Rise at lat 3°15′N, long 159°11′E from a depth of 3, 490m. Furthermore, the fluctuation patterns of the appearance percentage of gravel in each of the basins are similar to one another, which suggests a common sedimentation related to the global paleoclimate in the basins of the same drainage system. Spectral analysis using the Maximum Entropy Method (MEM) reveals that the appearance percentage of clay and sand in the Osaka basin each have a preeminent period of about 30m, while gravels in the northern part of the Kyoto basin and the Kameoka basin have a 12-13m period in common.
In order to re-examine an earlier theory on the subdivision of the soft sediment which is sometimes called “Alluvium” in enclosed coastal seas, an acoustic survey was carried out in Osaka Bay. Although the tools which were used for the surveys differ, the depths of acoustic reflectors in the old and the new records correspond well. The results of the new acoustic survey and drilling show good correlation between the depths of the reflectors and those of tephra seams and facies boundaries, for example, between those of mud and sand or those of sand and gravel. The earlier stratigraphic subdivision was based chiefly on differences in reflection patterns; the importance of reflectors as time markers was neglected. Consequently, the boundary between Alluvium A and Alluvium B in the earlier stratigraphy apparently crosses some reflectors. The distribution boundary between Alluvium A and Alluvium B on the sea floor was regarded as corresponding to that between sand and mud in the same area. This is, however, not correct. The combined thickness of Alluvium A and Alluvium B, which was supposed to equal that of total “Alluvium”, only corresponds to that of the upper and middle muddy parts, excluding the channel areas. On the basis of these facts, stratigraphy in enclosed coastal seas can be better understood, as follows. Unconsolidated muddy sediment, which forms the upper and middle parts of “Alluvium” in Japanese enclosed coastal seas, cannot be stratigraphically subdivided. The sandy part near the channel area and the muddy parts in the central bay and the area far away from the channels (both on the bottom surface) are in the relation of a contemporaneous heterotopic facies. The most obvious reflector in the acoustic record, which had been regarded as the boundary between “Alluvium” and the underlying strata, is better understood as the boundary between the upper and middle muddy “Alluvium” and the underlying “lower Alluvium”. The previous stratigraphy for the subdivision of unconsolidated sediment in other enclosed coastal seas around the Japanese Islands should be corrected in a similar way.
Organic carbon contents of two piston cores from the southern part of the Japan Sea are closely related with the lithology and relative abundance of a benthic foraminiferal species, Bolivina pacifica. That is, the organic carbon content is high in the layers of homogeneous clay, intensive burrowed clay, and thin-laminated clay with abundant occurrence of Bolivina pacifica, but low in the layers of weak burrowed clay and thin-laminated clay without benthic foraminifera. The sequential changes of the organic carbon content for the two cores are similar to the general pattern of the oxygen isotopic curve in the open ocean. This suggests that the paleoceanographic change of the Japan Sea has been essentially controlled by the global climatic changes, which link with eustatic sea level fluctuations. The detailed paleoenvironmental change in the Japan Sea since the oxygen isotopic stage 51 (8.5ky B.P.) is reconstructed on the basis of the organic carbon content as well as the lithological and benthic foraminiferal faunal changes in the cores.