[in Japanese]

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The lower Pliocene Kiyosumi Formation in the middle part of the Boso Peninsula, central Japan, is mainly formed of sandstone-dominated flysch-type alternation attaining more than 850m in maximum thickness, and outcrops under the control of a pair of the east-west trending northern anticline and southern syncline. A depositional model was proposed previously by the present author that the turbidite sandstones in the formation were deposited by the turbidity currents which flowed from the central northern outlet of the forearc basin, named the Kiyosumi Basin, restricted by an outer ridge called the Mineoka Uplift Zone along the southern margin. As a different idea that the turbidite sandstones in the formation were formed by the turbidity currents from the western outlet, flowing eastward, was proposed recently, additional measurement of the paleocurrents of the turbidite sandstones was conducted in the lowermost unit among five units of the formation in the Seiwa Prefectural Forest where the unit is exposed widely. The thick turbidite sandstones attaining 300m in maximum thickness in the lowermost unit were exclusively distributed in the southern part of the basin along the syncline axis.
The results of the measurement of the paleocurrent based on the current ripple cross lamination in the turbidite sandstones indicate westward flows, not eastward, which support the previous depositional model by the present author that the turbidite sandstones in the unit were deposited by the turbidity currents which were introduced into the basin from the central northern outlet and flowed along the feeder channel developed in the eastern part of the peninsula and then flowed downward to the west in depressions developed along the southern syncline axis and deposited coarse-grained thick turbidite sandstones there.

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To estimate the mechanism of dynamic in sediment quality relative to eutrophication, we compared several parameters and characterized the sediments in Kagoshima Bay. This study analyzed sedimentary organic matter and acid volatile sulfide (AVS) as possible indicators of eutrophication. The sediment samples were collected in the months of July, 2001 and August, 2002. Organic matter and AVS concentrations of the sediments showed heterogeneous horizontal distribution and did not appreciably change over a period of one year. The ignition loss (IL) concentrations ranged from 1.1% to 13.4%, while total organic carbon (TOC) and total organic nitrogen (TON) ranged from 0.2% to 2.3% and 0.04% to 0.22%, respectively. Higher values for IL, TOC and TON were observed in various stations of the inner area and in deep basin stations of the central area of the bay. The parallel increase in TOC and TON with IL suggested that the distribution profiles of TOC and TON in the sediments should be closely associated with IL. Concentrations of AVS ranged from 0.01mg/g to 2.2mg/g of sediment (dry weight) with high values observed in the deep basin of the inner area. Vertical distribution analysis showed decreasing concentrations of IL, TOC and TON with increasing sediment depths in the inner parts of the bay. On the other hand, no marked differences among sediment depths in concentrations of these parameters were observed in the central area. These results give the clear picture of the horizontal and vertical characterization of sediment in Kagoshima Bay. These also indicated that organic matter and AVS concentrations could be used as indicators for assessing environmental quality of Kagoshima Bay.

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This study aims to quantify the level of heavy metals in the sediments from the central west coast of Cebu, Philippines where previous Cu mining activity downloaded waste through the Sapangdaku River and the tailings outfall located at Ibo town. The surface sediments collected from the study area were analyzed for grain size fraction, total organic carbon (TOC), CaCO₃ and total heavy metals (Cu, Zn, Pb, Co, Ni and Fe).
Our results showed that the majority of the surface sediments were dominated by coarse fraction (>80% sand, <20% silt and clay). The range of TOC content in the surface sediments was found to be 0.08-2.71%. The variability of TOC can be attributed to variable sources of organic matter along the coast, and to the silt and clay fraction in the sediments. The CaCO₃ content in the surface sediments from the northernmost and southernmost parts of the study area was high (>10-60%) due to the abundance of calcite. The heavy metal content in the surface sediments from the tailings outfall in Ibo were higher compared to the other samples (Cu=>700ppm, Zn=>100ppm, Pb=>10ppm, Co=>30ppm, Ni=>20ppm and Fe=>5%). The concentration of heavy metals decreased towards the northern and southern parts of the area. The calculated Enrichment Factor (EF) showed that the heavy metals were highly enriched in the surface sediments from the tailings outfall in Ibo and near the mouth of the Sapangdaku River.
The enrichment of metals in the sediments from Ibo indicates an anthropogenic impact. In contrast, enrichment of metals from the mouth of the Sapangdaku River is believed to be dominantly natural; the mixing of fresh water and seawater might have accounted for the deposition and accumulation of these metals. The correlation of silt and clay fraction and heavy metals suggest that grain size fraction and Fe scavenging play major roles in the abundance and distribution of metals in surface sediments in the study area.

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Microorganisms growing in a stream often form biofilm draping the surface of riverbed gravels. The biofilm develops a particular interface between stream water and riverbed, which seems to control the hydrodynamic condition and the retention time of particles within the zone of interface. We made a series of experiment on the deposition of inorganic suspended particles from flowing water on the bed with/without biofilm using an open flume. Grain-size analyses of the deposits were done after experiments, and cross-section of the biofilm was observed. The increase of the sediment on the biofilm was proportional to the flow velocity, while that on no-biofilm bottom was decreased with the increase of the flow velocity. When the velocity increased, grain-size distribution of the sediment on the biofilm becomes coarser. The results indicate that the biofilm has a great advantage on the deposition of fine clastics from flowing water through sieving the particles by its mesh structure within biofilm.

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Usage and advantages of an application program “STube”, which is newly written in Java, for settling tube grain-size analysis is described. The program has all functions necessary for the analysis. Especially, it has usefull utilities such as: 1) choice of calculation for the relation between settling velocity and grain-size, 2) statistic parameters of grain-size distribution and errors, 3) drawing of histogram, cumulative curves of measured data as various graphs. In addition, it runs on multiplatform, and is installed and updated automatically through the Internet.

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