The Ryukyu Group, consisting of Pleistocene reef complex deposits that laterally pass into terrigenous sediments, crops out on Toku-no-shima, Ryukyu Islands, southwestern Japan. We propose a major revision of the previous stratigraphic scheme for the Ryukyu Group and provide a formal stratigraphic description. The Pleistocene sequences comprise the Tokunoshima and Metegu Formations, in ascending order, on this island. The Tokunoshima Formation reaches 140 m in thickness and is exposed extensively, covering peripheral areas of the island at elevations less than 210 m. It is divisible into two units, each consisting of proximal coral limestone and distal rhodolith, Cyclo-clypeus-Operculina, and detrital limestones. The Metegu Formation resting unconformably on the Tokunoshima Formation is composed mainly of thin (< 5 m) coral limestone. It is exposed at limited outcrops in southern parts of the island, ranging in elevation from 20 to 60 m. Stratigraphic position, known age-diagnostic nannofossils, and uranium-series and ESR dates indicates that the Tokunoshima Formation may be correlative to the main body of the Ryukyu Group on Okierabu-jima and Yoron-jima. An ESR date denotes that the Metegu Formation accumulated at > 146 ka.

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Cretaceous granitoids are widely exposed on the northern part of Kyushu Island, and are divided into the tonalite-granodiorite and the granite series, based on the petrographical and geochemical characteristics. The Itoshima and Fukae masses belonging to the tonalite-granodiorite series are significantly voluminous in the Cretaceous granitoids in this area. They correspond to the magnetite-series granitoids, and are characteristically high in Sr. The Itoshima mass geologically surrounds the Fukae mass. The boundary between both masses is gradational. The Itoshima mass is lithologically subdivided into ITO-and ITO-2. ITO-1 contains euhedral hornblende, and is characterized by a preferred orientation of hornblende, biotite and plagioclase. ITO-2 has the same mineral assemblage as ITO-1 but more leucocratic, and is weakly foliated. The Fukae mass shows massive leucocratic lithofacies lacking hornblende. It corresponds to trondhjemite in terms of modal composition. ITO-1 gradually changes into the Fukae mass with decrease in modal hornblende through ITO-2. The bulk chemistry of both masses forms continuous trends in the variation diagrams, suggesting magmatic differentiation, which can be modeled by the fractional crystallization mainly of hornblende + biotite + plagioclase + titanite + magnetite in the early stage, and biotite + plagioclase + magnetite in the later stage. Inferred crystallization depth of the Itoshima mass using the total-Al in hornblende geobarometer is ca 0.6 GPa, which is equivalent to mid-crustal depth. This estimation is supported by the presence of magmatic epidote. In the discrimination Sr/Y-Y diagram, the samples of the Fukae mass are plotted on the adakite field, whereas the Itoshima mass falls within the island arc field. The Fukae adakitic magma could therefore be derived from the dacitic Itoshima magma by a fractionation under the middle crust conditions.

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We analyzed 27 elements of the river-bed sediments and soils in the Watarase-river basin and the Miyata-river basin using XRF briquet method. The Watarase-river basin has been seriously polluted by the past works of the Ashio copper mine. The pollution levels of As, Cu, Pb and Zn are still high at the present time in the Watarase-river basin even in the rice field compared with environmental standards of soil. These elements are originated from ore minerals of the Ashio copper mine. The Miyata-river basin has also been polluted by the past works of the Hitachi mine. Presently, the pollution of the river-bed sediments of the middle reaches by As, Cd, Cr, Cu, Ni, Pb, S and Zn is stronger than the sediments of the upper stream near the mine. These elements are derived from slag is originated from the smelting at the Hitachi mine refinery. A mountain of slag is deposited near the river, and the slag flows out into the Miyata-river.

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The focus of this study is a redox front formed along a fracture within the last ca. 10⁵ y that is estimated by the geological setting and the features of the redox front's spatial pattern in Tertiary tuffaceous sedimentary rock distributed in central Japan. In this investigation, the redox band has been analyzed by XRF, EPMA and SEM-EDS for major and trace elements to understand the elemental profile, and the spatial distribution of elements from the fracture to the rock matrix. The XRF analysis showed that Mn is concentrated in three sharp layers, situated near the fracture surface. In contrast, the most Fe-concentrated layer was seen in deeper part of the rock matrix. This suggests that fractionation between Mn and Fe has occurred during the front migration. The Mn-concentrated layers are accompanied by the enrichments of various trace elements such as Zn, Ni, Ba and Y. On the other hand, the Fe-concentrated layer is characterized by enrichments of P and also Y. EPMA analysis revealed that the Fe is distributed heterogeneously in the rock matrices with high P enrichment. Detailed SEM observation identified that fossilized microbe colonies occur in the pore space. Direct examination of the fossilized cell like structure with SEM-EDS showed that they are composed exclusively of Fe and Si. This observation and the results of incubation experiment suggest that the microbial activity played an important role in the concentration of Fe and other elements in the redox front under low temperature subsurface condition. These lines of evidence can be used as chemical analogues of long-term contaminant fixation by the redox reaction that may occur in the geological environment surrounding almost any type of subsurface waste repository.

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A tectonic slice consisting of sheeted dikes has been found in the Oku-Niikappu Dam Complex (ONDC), a mid-Cretaceous accretionary complex in the Idonnappu Zone, Hokkaido. The sheeted dikes are composed of gabbroic to diabasic rocks with relict clinopy-roxenes showing a character of island arc and transitional from arc to oceanic tholeiites. The dikes are considered to have originated from an intraoceanic remnant arc which was finally accreted, forming the ophiolitic assemblage of the ONDC. Pre-subduction exposure of the sheeted dikes in an pelagic environment, as suggested by the presence of gabbroic clasts in the oceanic debrite, allowed accretion of the sheeted dikes to the continental margin.

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The mid-Cretaceous Oku-Niikappu Dam Complex (ONDC: Fig.1) occurs in the Niikappu River area of the Idonnappu Zone (Ueda and Miyashita, 2002, 2003). The ONDC contains a tectonic block with a stratigraphic succession from basal volcanic rocks through alternating conglomerate and chert (middle unit) to an upper chert unit (Figs.2-4). The conglomerate clasts consist dominantly of basaltic to rhyolitic volcanic rocks, with subordinate of ultramafic to felsic plutonic clasts (Figs.3 and 5). The basal volcanics and the volcanic clasts in the conglomerate have chemical characteristics of island arc origin. This succession represents an island arc in which activity ceased, followed by dissection in a pelagic environment, and is suggestive of an intraoceanic remnant arc isolated by back-arc spreading. Similar strata and clastic compositions have been reported from the remnant arcs of the Daito and Kyusyu-Palau Ridges in the Philippine Sea Plate. The occurrence of accreted remnant arcs is significant for considering subduction zone tectonics, because they indicate subduction of oceanic crust associated with island arcs and back-arc basins similar to those of the present-day Western Pacific.

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