Bottom Sediments of the Jyoga-seto Channel, Iki Island, Nagasaki Prefecture, Kyushu, Japan

The bottom sediments in the Jyoga-seto channel, western Iki Island, Kyushu consist mainly of organic calcareous debris. Coarser sized and ill-sorted sediments are found on the narrow submarine channel located in the east-side of Jyoga-seto channel, while finer sized and well-sorted sediments are widely distributed on the submarine sand bank in the west-side of Jyoga-seto channel. The calcareous sediments on the submarine sand bank may have originated at the northern end of this area. The shell fragments are transported onto the sand bank by the tidal current of which the flow from the north is slightly stronger than south flow. This southward tidal current may affect the sorting and kurtosis of the biogenic sand on the submarine sand bank in the Jyoga-seto channel

Submarine Geology of the Aba Bay, the Environs of Nagasaki City, Kyushu. - Study on the Yagami Coal-field. Part 2 -

Coastal configuration and submarine topography in the southern parts of the Yagami coal-field, eastern environs of Nagasaki City, controlled by the geologic structures of the Paleogene formations and the distribution of neo-volcanics. The neo-volcanics of the Makishima Island, east of the Aba Bay, may be belonging to the Nagasaki volcanic group by its petrographic features. This fact is suggesting that the Paleogene coalbearing formations may be distributing under these volcanics and. extending to the seawards. The Aba Bay originally constructed by the faults of north-south trend, cut in the Paleogene strata, and lately submerged by the upheaving of the sea level of at least 40 meters. 30 bottom sediment samples from the Aba Bay area are treated by the mechanical grain analysis. The division of the sediments which was proposed by Inman and Chamberlain (1955) are applied to this area. The coarse sediments containing organic calcareous fragments which are designated to Sediment Type V are found in the coastal area where strong influence of surf and tidal current affecting. Muddy sediments are classified to Types IIIa, III and IIIb. Fine mud found in the deeper part of the bay mouth and also in the north-western part of the bay head and the shallow embayment in the Makishima Channel. These fine-grained sediments may be yielding under the stagnant water body or lower part of circulation current in the bay. The diagrams of sand-silt-clay ratios are most useful for the division of the muddy sediments. In the longitudinal section of the Aba Bay, the amount of silt and clay increasing with distance from the bay head and water depth

Specific Gravity and Absorption of Volcanic Rocks distributed in Middle and Northwestern Parts of Kyushu, Japan

The specific gravity and absorption of water of 70 volcanic rock samples which were collected from the middle and northwestern parts of Kyushu were measured. The volcanic rocks in this surveyed area were classified into three volcanic rock series, namely, San-in, Hohi and Continental, depend upon the geologic stages of their volcame activities and lithologic characters. The San-in volcanic rock series (late Pleistocene to Recent) which is composed chiefly hornblende andesite has light specific gravity and high percentage of absorption. On the other hand, the Continental volcanic rock series (late Miocene to Pliocene/ or Plistocene) which is composed basalt has heavy specific gravity and small quantity of absorption. The Hohi volcanic rock series (early Pleistocene) is characterized by the cosisting of pyroclastic rocks and the pyroxene andesite lava flows. The Hohi volcanic rock (so-called Chikushi lava) has intermediate values of specific gravity and absorption between those of the San-in and the Continental. The increase of specific gravity according to the volcanic rock series from acidic to basic have a close relationship with the decrease of absorption of water

Paleogene Stratigraphy of the Higashi-Nagasaki-machi district, Yagami Coal-field, Nagasaki Prefeture. -A Study on the Yagami Coal-field. Part 1-

The Paleogene strata distributed in the Yagami coal-field, the environs of Nagasaki City, is classified into the following nine formations in descending order : Yagami group (Thickness in meters) Johira formation 30+ Akamatsu formation 180 Tachi formation 120 Koga formation 40 Kirimiya formation 120 Saburaishi formation 30 Isahaya group Keya formation 320 Kakido formation 80 Enoura formation 250+ From the characters of the stratigraphic succession and the molluscan or foraminifereral assemblages, the Isahaya group is correlated with the upper half of the Hondo group in Amakusa and the Yagami group is correlated, with the Iojima group in the Takashima coal-field. Some bio-stratigraphic problems of the Paleogene mega-fossil zone in northern Kyushu is also discussed here

Review of the Methods of Grain-size Analysis of Sediments and its Computer Applications

The present study is a review of the methods for grain-size analysis in clastic sediments, and some problems by the sieving and pipette methods are discussed. The problems of the sieving method are in the accuracy of the mesh opening, the length of working time and the kind of sediments. To maintain correct sieving, about 20 minutes is required for the working time. But, in some sediments with abundant organic calcareous fragments that were broken down for a long time, the sieving time should be kept within 20 minutes. The pipette method is good for the analysis of muddy sediments, but it requires much labor, takes a long time, and is apt to be affected by the temperature of the fluid and the heterogeneity of the particles in the fluid. By the application of the FORTRAN computer program, the authors hope to undertake further comparative studies of grain-size analysis

Bottom Sediments and Shell Remains from Mogi Area in Chijiwa Bay, Kyushu

Fourty one bottom sediment samples for mechanical and faunal analyses were collected from the western part of the Chijiwa Bay which covers an about 60 sq. km area off Mogi, Nagasaki City. The bottom sediments were divided into four sediment types and their areal distributions are shown in figure 5. A narrow belt of sandy silt classed as Type III is found in the western half of the shllow submarine valley and separates the near- and offshore sandy sediments classed as Type II or IIIa. Fourty two pelecypod molluscan species which are listed in Table 2 were discriminated from the unit sediment samples (200cc wet volume sediment) and eight predominant species were selected as shown in Table 3. The dominant molluscan remains were found in the silty sand of Type IIIa which represents a transition between muddy and sandy sediments

Bottom Sediments and CHN Contents of the Imari and Omura Bays, Northwestern Kyushu, Japan

The grain-size parameter, calcium carbonate content and carbon, hydrogen and nitrogen contents of 51 bottom sediment samples obtained from the Imari and Omura Bays, northwestern Kyushu, were determined. The bottom sediments in outside of the Imari Bay chiefly consist of sand with a high content of calcium carbonate of 60.35% in average and a small amount of CHN, 0.83% on the average. On the contrary, the silty sediments were widely distributed in the inside of Imari Bay and have a low content of calcium carbonate of 27.08% and high content of CHN, a 3.10% average. The silty clay and fine silt are the most abundant bay sediments in Omura Bay. These fine-grained sediments have an average of 28.29% of calcium carbonate content and 3.17% of total CHN content, similar to the inside of Imari Bay. The average carbon-nitrogen ratio of the sediment samples from the outside and inside of Imari Bay and Omura Bay are 8.41, 12.30 and 8.90 respectively. A part of the unusual high content of the organic carbon and the high value of carbonnitrogen ratio inside of Imari Bay are from the fine fragments of coal which were discharged from the coal-mines worked along the coast of the Imari Bay up to about twenty years ago