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In Japan, high-level radioactive waste and specific low-level radioactive waste which includes long-lived radionuclides are planned to be disposed of in the geological formations at depths greater than 300 m. The disposal site will be selected through a stepwise site investigation process that consists of a Literature Survey, Preliminary Investigation, and Detailed Investigation phases. In October 2020 a Literature Survey was launched in Japan at two municipalities in Hokkaido for the first time since NUMO initiated a nationwide call for volunteer municipalities in 2002, and the outcomes are currently being compiled. To enhance the public's understanding of how to implement safe geological disposal in Japan based on the latest scientific knowledge and technology, NUMO, as the implementing organisation, developed and published a safety case for geological disposal at the pre-siting stage. This safety case provides multiple lines of arguments and evidence to demonstrate the feasibility of the geological disposal and a basic structure for a safety case that will be applicable to any potential sites in Japan. The safety case also presented some R&D challenges to enhance the technical confidence of the project, including the R&D topics related to rock mechanics. This report presents the current status of the geological disposal programme in Japan, together with the status of the Literature Survey phase and an overview of the NUMO safety case. [ABSTRACT FROM AUTHOR]

The results of pioneering carbon dioxide capture and storage （CCS） projects such as Sleipner and Gorgon are widely recognized as milestones in the early days of CCS. The reservoir formations of the pioneering projects are characterized by homogeneous sandstones that develop over several hundred meters thick. On the other hand, sandstone formations expected to work as reservoirs for CCS in Japan are characterized to be more heterogeneous and thinner than those of pioneering projects as above because of the tuffaceous sandstones typical of volcanic arcs. In addition, the geological formations in Japan that separated by complex faults in active continental margins might not be suitable for CCS reservoirs. However, we will have to make CCS feasible against these "challenging" formations. In this paper, examples of multidisciplinary approaches for geological evaluation of domestic depleted oil fields obtained from a joint study with INPEX are shared, and we hope that those findings would help future CCS projects in Japan. [ABSTRACT FROM AUTHOR]

The empirical relationship between the porosity and P‐wave velocity is a useful tool for probing large‐scale underground physical properties and stress states based on P‐wave velocity structures acquired by seismic surveys. In this study, the porosity‐velocity curves were examined using local core sample and logging datasets acquired along the Kumano transect in the Nankai Trough, Southwest Japan. We tested Hashimoto et al.'s (2010) hypothesis that slope apron and accreted sediments have different relationships. Our advantage is using a large amount of logging and core data obtained at multiple sites in the Nankai Trough under various geological conditions, from the incoming oceanic plate to the inner wedge. We identified multiple types of porosity – P‐wave velocity relationships: 1) The first type agrees with the low‐velocity model in the global empirical relation of Erickson and Jarrard 1998), which is observed at lithostatic stress state condition (incoming upper Shikoku basin and slope sediments), 2) The second type consistent with high‐velocity models of the global empirical relation observed at compressive stress state condition (accreted sediments), which have a higher velocity and larger dependence on the porosity than the first type with the same porosity, and 3) The third type for incoming sediments with high smectite content has lower velocity than the first type. Based on our results, the transition between the first and second porosity – velocity relationships occurs in the prism toe, implying that compressive stress due to subduction controls acoustic properties and the lithification process of these sediments. Plain Language Summary: Physical properties of rocks in subduction zones are important factors controlling genesis of earthquakes. Among many kinds of physical properties, this study focuses on the relationship between porosity and P‐wave velocity at the Nankai Trough, Southwest Japan. As this relationship is affected by how the soft sediments are lithified through the subduction process, it has been studied frequently to understand physical properties and stress states of geological formations around plate boundary faults. This study compiles P‐wave velocity datasets acquired by scientific drilling projects in offshore regions, as well as porosity datasets. We tested the hypothesis proposed by a previous study that there are two types of the relationships between the two quantities. We find these two types are consistent with the global empirical relationships observed at lithostatic and compressive stress states respectively. The former includes sediments on the oceanic plate before subduction and slope apron sediments. The latter are sediments accreted toward the Japan arc. We also find that the transition from the former to the latter occurs in the sediments at the tip of accretionary prism. This suggests that compressive stress state due to subduction plays an important role in controlling the acoustic properties of sediments. Key Points: Porosity and P‐wave velocity data were compiled to investigate their relationships at the Kumano transect in the Nankai TroughAccreted sediments have higher P‐wave velocity compared with incoming and slope apron sediments with the same porosityThe stress state in the accretionary prism might be a factor controlling the porosity – P‐wave velocity relationships of sediments [ABSTRACT FROM AUTHOR]

Understanding the causes of the Sino‐Japanese disjunctions in plant taxa has been a central question in eastern Asian biogeography, with vicariance or long‐distance dispersal often invoked to explain such patterns. Diabelia Landrein (Caprifoliaceae; Linnaeoideae) comprises four shrubby species with a Sino‐Japanese disjunct distribution. The species diversification time within Diabelia, covering a long geological history of the formation process of the Sino‐Japanese flora, dated back to the middle Oligocene, therefore, Diabelia would be an ideal model to elucidate the biogeographic patterns of Sino‐Japanese disjunctions with climate fluctuation. In this study, we analyzed complete plastome sequence data for 28 individuals representing all four species of Diabelia. These 28 plastomes were found to be highly similar in overall size (156 243–157 578 bp), structure, gene order, and content. Our phylogenomic analysis of the plastomes supported a close relationship between Diabelia ionostachya (Nakai) Landrein & R.L. Barrett var. wenzhouensis (S.L. Zhou ex Landrein) Landrein from eastern China and Diabelia spathulata (Siebold & Zucc.) Landrein var. spathulata from Japan. Diabelia serrata (Siebold & Zucc.) Landrein was identified as sister to a population of Diabelia sanguinea (Makino) Landrein from Tochigi in central Japan and D. spathulata Landrein, from Toyama, central Japan. Most Diabelia lineages were estimated to have differentiated 8–28 Mya. Our results indicate that two independent vicariance events could explain the disjunction between Japan and Korea in the mid to late Miocene, and between Zhejiang and Japan in the early Miocene. [ABSTRACT FROM AUTHOR]

We applied advanced surface wave analysis for multichannel and multishot seismic data to estimate S-wave velocity structure with high lateral resolution. Although a horizontally layered structure is typically assumed in surface wave analysis, this assumption might be violated in environments such as geothermal fields because of their heterogeneous geological formation. The lateral variation of phase velocity can be effectively estimated with common midpoint (CMP) cross-correlation (CMPCC) analysis. In this study, we introduced two additional approaches into the CMPCC analysis workflow, to further improve lateral resolution of phase velocity estimates. One approach is window-controlled CMPCC analysis, which applies a spatial window for the CMP gathers while maintaining the accuracy of the phase velocity estimates. In this analysis, we found that it is difficult to improve phase velocity estimates at lower frequencies, as a wider spatial window must be kept to maintain the accuracy of the dispersion curve. Therefore, we introduced another approach in which we consider the direction of surface wave propagation from sources to receivers. Selection of cross-correlations based on source–CMP direction provides a significant improvement in dispersion curve resolution in the presence of lateral velocity variations, for a wide frequency range. We applied direction-controlled CMPCC analysis to seismic data acquired in the Yamagawa geothermal field, Kyushu Island, southwest Japan, and obtained dispersion curves in the heterogeneous geological setting. We then obtained S-wave velocity profiles by applying genetic algorithm inversion to the dispersion curves. The S-wave velocity profiles in the geothermal field resolve shallow and local heterogeneous structures (e.g. volcanic ash, pumice and igneous intrusions) that cannot be identified on reflection seismic profiles. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Position-by-position t-T paths are reconstructed from thermochronological data. • Position-specific t-T paths reflect the formation history of the pluton. • It is a new method for understanding of fracture populations in granite. • The t-T path evaluation provides key insight to investigate fracture frequency. Abstract Understanding the locational differences of time-temperature (t-T) paths within the granite contributes to clarifying the detailed formation history, especially the thermal evolution, of the entire pluton after the incipient intrusion of the granitic magma into the shallow crust. The position-by-position t-T paths of fifteen samples of the Toki granitic pluton, central Japan, are reconstructed from thermochronological data, including zircon U–Pb, biotite K–Ar, zircon fission-track (ZFT), and apatite fission-track (AFT) ages, FT length characterization, and FT inverse calculation. In case of sample No. 1, the t-T path consists of zircon U–Pb ages (74.0 ± 1.1 Ma and 72.6 ± 1.7 Ma), a biotite K–Ar age (73.0 ± 1.8 Ma), a ZFT age (57.2 ± 2.3 Ma), an AFT age (41.5 ± 2.7 Ma), and the FT inverse calculation. The t-T paths show position-specific characteristics that reflect the history of the pluton after the incipient intrusion of the granitic magma into the shallow crust. Shallow parts of the western and northeastern margins of the pluton show rapid cooling from the intrusion stage to the ZFT partial annealing zone (PAZ), and thus represent position-specific characteristics in relation to crustal assimilation in the intrusion/emplacement processes. The cooling behavior around the condition of AFT PAZ was interpreted as a reflection of regional tectonic exhumation of the pluton. This study also presents useful knowledge to evaluate fracture populations in a granitic pluton. The relationship between the position-specific t-T path and fracture frequency (fracture number per unit interval) provides a criterion for evaluating the fracture population of the granitic pluton, called 'thermochronological evaluation', which is a key insight to investigating fluid flow and mass transfer in the rock mass. The t-T path shows whether cooling was slow or rapid from thermal conditions of solidification/crystallization to the biotite K–Ar closure temperature; parts of the pluton that cooled slowly correspond to parts with high frequencies of fractures, and vice versa. The absolute value for duration between the zircon U–Pb age evaluated from the oscillatory-zoned area (OZ age) and biotite K–Ar age shows high correlation with fracture frequency (R 2 = 0.89), and thus gives a quantitative indicator for evaluating fracture frequency; longer duration accompanies higher frequency. A combination of thermochronological evaluation, the local cooling indicator, and the lithofacies effect can be applied as potential diagnostic tools for detailed evaluation of the fracture population. [ABSTRACT FROM AUTHOR]

A groundwater dating for very old porewater using 36Cl and 4He was applied to the Koetoi and Wakkanai formations distributed in the northernmost part in Japan. Measured 36Cl/Cl in the Koetoi Formation was 2.6 ± 2.0 × 10−15 and that in the Wakkanai Formation was 8.1 ± 2.5 × 10−15. These values are similar to 36Cl/Cl in situ secular equilibrium calculated from chemical compositions of core suggesting that Cl− ions and porewater have remained in the formations for much longer than half-life of 36Cl . He concentration in porewater ranged from 1.1 × 10−6 to 2.6 × 10−5 (ccSTP gw-1) and it is much higher than water saturated with air indicating that both formations contain very old porewater. However, the possibility of mixing of young water was indicated because He concentration was lower than that calculated by multiplication of in situ He production and time after the uplift. This possibility was also supported by Cl−, δD, and δ18O data. After combining information on 36Cl/Cl, 4He, and δD and δ18O, it was inferred that the porewater in the deep part of the Wakkanai Formation might have been stagnant since the uplift. The porewater in the Koetoi Formation and the shallow part of the Wakkanai Formation were found to be affected by young surface water. [ABSTRACT FROM AUTHOR]

The Chiba composite section of the Kokumoto Formation in central Japan is a remarkable, thick marine succession and is a candidate for formal recognition as the Global Boundary Stratotype Section and Point (GSSP) for the base of the Middle Pleistocene stage. Although there have been numerous studies of the Kokumoto Formation, the sedimentology of the formation, particularly in the Chiba composite section, has been unclear. We use field observations and laboratory analyses to elucidate the sedimentary processes and depositional environments of the formation. The Chiba composite section includes the Matuyama–Brunhes paleomagnetic reversal, which is the primary guide for the Lower–Middle Pleistocene boundary, along with multiple tephra deposits that provide isochronous correlational tie points. One bed, Byk-E (also known as Ontake-Byakubi Tephra), immediately underlies the paleomagnetic reversal and hence provides a useful widespread marker for the boundary. The predominant silty beds of the Chiba composite section are intensely bioturbated and lack evidence of episodic deposition such as slumps or muddy turbidites. However, minor sandy beds intercalated within the silty section, particularly in its lower part, are either (1) fining upward sequences with faint planar or ripple laminations and an erosional base, or (2) sequences containing abundant mud clasts in a poorly sorted sand matrix with a sharp base and an irregular top surface. The silty beds are interpreted to be hemipelagite formed by deposition of fine-grained suspended material under stable and calm bottom-water conditions. The sandy deposits are interpreted to be sediment gravity-flow deposits (i.e., turbidites and debrites). These sedimentary processes and the trace fossil assemblage indicate that the Chiba composite section was formed in a continental slope environment. The depositional environments of the Chiba composite section, together with tephrostratigraphy, make it suitable for high-resolution studies on the paleoenvironment, paleoclimate, and paleoceanography of the northwest Pacific Ocean across the Lower–Middle Pleistocene boundary; it is therefore a suitable candidate to become the GSSP for the Middle Pleistocene. [ABSTRACT FROM AUTHOR]

The expected geomorphic after-effects of the M w 9.0 Tōhoku-oki earthquake of 11 March 2011 (eastern Japan) are summarized by a schematic model of seismic driving, which details seismogenic disturbances to sediment systems that affect the rate or timing of sediment delivery to coastlines over timescales of 10 2 –10 4 years. The immediate physical environmental responses to this high-magnitude earthquake included a large tsunami and extensive region-wide slope failures. Normally, slope failures within mountain catchments would have significant impacts on Japan's river and coastal geomorphology in the coming decades with, for example, a new beach ridge expected to form within 20–100 years on the Sendai Plain. However, human activity has significantly modified the rate and timing of geomorphic processes of the region, which will have impacts on likely geomorphic responses to seismic driving. For example, the rivers draining into Sendai Bay have been dammed, providing sediment traps that will efficiently capture bedload and much suspended sediment in transit through the river system. Instead of the expected ~ 1 km of coastal progradation and formation of a ~ 3 m high beach ridge prior to the next large tsunami, it is likely that progradation of the Sendai Plain will continue to slow or even cease as a result of damming of river systems and capture of river sediments behind dams. The resulting reduction of fluvial sediment delivery to the coast due to modification of rivers inadvertently makes seawalls and other engineered coastal structures even more necessary than they would be otherwise. [ABSTRACT FROM AUTHOR]

Manganese (Mn) carbonate nodules, which differ from seafloor Mn nodules mainly composed of MnO 2 , are occasionally embedded in the form of a lens shape in the Jurassic accretionary complexes, such as the Mino Belt in Japan. The interpretation of the formation process of Mn carbonate is still controversial, particularly concerning whether the Mn carbonate was formed primarily or secondarily. In this study, a fresh Mn carbonate nodule incorporated into the red siliceous mudstone was collected for geochemical and sedimentological analysis. The optical observation of thin sections indicates that the Mn carbonate nodules are composed of abraded grains of rhodochrosite spherule with radiolarians and are sedimentary embedded in siliceous mudstone. Microfossil radiolarians from the Mn carbonate nodules and the host red siliceous mudstone are dated as the Bajocian, but the radiolarians in the nodules are somewhat older than those in the host red siliceous mudstone. Geochemical analysis using the X-ray absorption near-edge structure on Ce indicates the dominance of trivalent Ce at present, despite the observation of a positive Ce anomaly in the PAAS-normalized REE pattern of Mn carbonate. The REE adsorption experiment on synthesized MnCO 3 does not show any distinctive positive Ce anomaly, and a thermodynamic calculation suggests the possible coexistence of rhodochrosite and spontaneous oxidation of Ce. A leaching experiment that can selectively decompose the carbonate phase demonstrated no Ce anomaly in the carbonate phase of the Mn carbonate and a poor contribution to the bulk REE concentration. The carbon isotope data of Mn carbonate nodule implied the dominance of inorganic marine carbonate origin with small contribution of organic decomposition. The most plausible account of all of the observational and geochemical results is that the rhodochrosite grains were primarily formed on the depositional site and subsequently transferred to a different site, where siliceous mudstone was deposited. [ABSTRACT FROM AUTHOR]

Despite the well-reconstructed paleoceanography of the late Quaternary deposits in the East (Japan) Sea (ES), provenances of terrigenous sediments and a comprehensive interpretation of their variations since the Last Glacial Maximum remain unclear, especially in regard to the mainland China- and Taiwan-derived matter. Grain size, conservative trace elements, rare earth elements (REEs), Nd isotope, and clay mineralogy of core sediments from the Ulleung Basin of the ES were investigated for better understanding of detrital sediment provenance and transport process and then their forcing mechanisms over the last 21 kyr. Geochemical–mineralogical multi-indices in this study showed notable three-phase changes in sediment provenance, which can be closely related to sea-level fluctuation, development of the Tsushima Warm Current as well as intermittent influence from the East Asian summer monsoon climate evolution. During Unit 1 (21.1–8.4 kyr BP) when the Tsushima Warm Current was absent in the ES, the paleo-Changjiang and the paleo-Huanghe mouth might be situated close to the study area and thus mainland China could have played major role in the southwestern Ulleung Basin sedimentation. In particular, the formation of rhythmic dark-colored alternation in Unit 1 is possibly attributable to the pulse of paleo-Huanghe discharge associated with centurial- to millennial-scale variability in the East Asian summer monsoon. In Unit 2 (8.4–7.2 kyr BP), these river mouths gradually retreated to their present positions with global sea-level rise, leading to decreasing terrigenous sediment supply from mainland China to the study area. Since 7.2 kyr BP (Unit 3), sedimentation in the Ulleung Basin should still be mainly derived from mainland China. Meanwhile, increasing chlorite/kaolinite ratio but decreasing ε Nd value revealed that terrigenous matter from Taiwan might have been limitedly transported northward to the study area by the fully evolved Tsushima Warm Current. A prominent decline in chlorite/kaolinite ratio, together with contrast change on ε Nd value, centered at around 2.9 kyr BP (3.3–2.4 kyr BP) may have been caused by the Tsushima Warm Current suppression, possibly related to the Pulleniatina minimum event popularly found in the study area and nearby seas. [ABSTRACT FROM AUTHOR]

Abstract: This paper focuses on the formation mechanism of fractures induced by excavation of a gallery in soft sedimentary rocks in the Horonobe area of Japan. Detailed fracture mapping of the gallery indicates that the fractures consist of both pre-existing shear fractures and excavation damaged zone (EDZ) fractures. EDZ fractures correspond to weak planes associated with bedding planes or transgranular cracks. The EDZ fractures terminate against pre-existing shear fractures. Therefore, even for excavations in soft sedimentary rocks, formation of the EDZ fractures are controlled by pre-existing fractures and earlier weak planes. [Copyright &y& Elsevier]

Abstract: We measured gas permeability of Neogene sedimentary rocks from Wakkanai, Koetoi and Yuchi Formations in the Horonobe area in northern Hokkaido, Japan. Measurements were done at room temperature and during pressure cycling to simulate underground conditions. Fresh intact samples from surface outcrops yielded a similar range of permeabilities as did intact samples from drill cores, within lithological variations. Comparison of laboratory and in-situ measurements has revealed that the permeability of Wakkanai Formation (middle to late Miocene, siliceous mudstone) from in-situ measurements is bounded by the permeability of brecciated specimen on the upper side and by the permeability of intact specimens on the lower side. Fragments in fault breccia are smaller than sample size and laboratory data should be applicable to natural fault rocks. Permeability of fractured specimens falls in between those upper and lower bounds, and complex scale issues will not be important in determining upper and lower bounds of permeability. The hydraulic conductivity values from in situ tests for Koetoi Formation (late Miocene to Pliocene, diatomaceous mudstone) are similar to those of the gas permeability of intact specimens. Effects of faults and fractures on permeability seems to be minor for this formation, and this was confirmed by permeability measurements with fractured samples. The hydraulic conductivity values from in situ tests for Yuchi Formation are lower than estimates from laboratory tests by within an order of magnitude. Thus permeability measurements in laboratory on fresh surface samples (intact, fractured and brecciated), combined with geological survey on the development of faults and fractures, leads to quantitative estimates, even if not complete, of underground permeability structures. [Copyright &y& Elsevier]

The paper addresses the composition and genesis of endogenous borates from hypabyssal skarn deposits of Japan (Honshu Island) that were formed after dolomitic, rhodochrosite, and calcareous marbles in the contact aureoles of magmatic intrusions of diverse felsicity (from granites to diorite-monzonites). Metasomatic bodies formed at the prograde stage of the mineral formation are characterized by clearly expressed zoning of primitive type. Borates occur in the calciphyres at the Neichi, Kaso, and Rito mines, and are developed in calcitic marbles at the Fuka mine. Depending on initial composition of carbonate rocks, borates are represented by suanite, kotoite, jimboite, and takedaite in the outer zones of spinel-forsterite and galaxite-jacobsite-tephroite calciphyres or calcitic marbles, respectively. It was shown that early borates are subjected to hydration that is expressed in variable deficit of boron. At the next stages of hydrothermal mineral formation, they are replaced by pertsevite, wiserite, sibirskite, and other borates. [ABSTRACT FROM AUTHOR]

Geological, paleontological, and geochronological studies of the Hida Gaien Belt were carried out in the upper Kuzuryu-gawa River area, northern central Japan. The Hida Gaien Belt lies between the Hida and Mino belts of Southwest Japan and is one of the most complex geologic belts in Japan. The geology of the following units in the study area, mostly bounded by longitudinal, high-angle faults, was particularly reexamined and described: the Ise metamorphic rocks, the Fujikuradani, Tomedoro, Oguradani, Motodo, Ootani, and Konogidani Formations, and the Tetori Group. Among them, the Tomedoro and Konogidani Formations are both composed mainly of greenstone, and were conventionally coupled together as 'the Tomedoro schalstein member' or 'the Konogidani Formation'. However, the conformable relationship between the Tomedoro Formation and overlying Middle Permian Oguradani Formation, and the K- Ar and 40Ar-39Ar ages of 75-69 Ma ( Late Cretaceous) from the basalt lava of the Konogidani Formation reveal that they are separate formations with different ages. The Oguradani Formation, consisting of limestone, shale, and sandstone with Middle Permian Boreal- Tethyan mixed brachiopod fauna, is correlated with the Moribu Formation in the Takayama area of the Hida Gaien Belt, and with the Middle Formation of the Maizuru Group in the Maizuru Belt. The Tomedoro Formation below the Oguradani Formation, in turn, is correlated with the Lower Formation of the Maizuru Belt. The new Late Cretaceous age data from the Konogidani Formation and presence of latest Cretaceous, post-tectonic volcanic rocks in the study area finally indicate that the fault-bound structure of the Hida Gaien Belt between the Hida and Mino belts was formed in a very short period in Late Cretaceous age. [ABSTRACT FROM AUTHOR]

After the severest mass extinction event in the Phanerozoic, biotic recovery from the extinction at the Permian-Triassic boundary required approximately 5 my, which covers the entire Early Triassic. It is important to obtain information on the superocean Panthalassa, which occupied most of the world ocean, to explore paleoenvironmental changes during the Early Triassic at the global scale. In order to establish the continuous lithostratigraphy of pelagic sediments in Panthalassa during the Early Triassic, high-resolution reconstruction of the Lower Triassic pelagic sequence in Japan was conducted for the first time based on detailed field mapping and lithostratigraphic correlation in the Inuyama area, central Japan. The reconstructed Early Triassic sequence is approximately 9.5 m thick, consists of five rock types, and is divided into eight lithological units. For the reconstructed continuous sequence, measurement of carbon isotopic composition of sedimentary organic matter (δ13Corg) was carried out. Stratigraphic variation of the δ13Corg value shows large-amplitude fluctuations between −34.4 and −21.0‰ throughout the sequence. In order to establish a higher resolution age model for the reconstructed Lower Triassic pelagic sequence, we correlated δ13Corg records in the Inuyama area with high-resolution isotopic profiles of carbonate carbon (δ13Ccarb) from shallow-marine carbonate sequences in southern China based on the similarity in general variation patterns with age constraints by radiolarian and conodont biostratigraphy. The result provides a high-resolution time scale for the pelagic sequence of Panthalassa during the Smithian and Spathian. The age model suggests a drastic increase in sedimentation rate during the late Smithian, which should have been caused by the increase in terrigenous input to this site. [ABSTRACT FROM AUTHOR]

Abstract: The Guadalupian paleo-atoll limestone (Iwato Formation) in SW Japan was primarily formed in low-latitude mid-Panthalassa and was later tectonically accreted to South China (Japan) margin during the Jurassic. The present biostratigraphic study clarified that the Iwato Formation consists of 5 biostratigraphical intervals; i.e. four fusuline assemblage zones (Assemblage zones 1 to 4) and a barren interval on the top. Assemblage zones 1 to 4 correspond to the Neoschwagerina craticulifera Zone, N. margaritae Zone, Yabeina globosa Zone, and Lepidolina multiseptata Zone of the conventional Tethyan fusuline stratigraphy, respectively. The present study newly clarified the following significant aspects of paleobiogeography of the Permian fusulines as to the extinction of large-tested taxa in the latest Guadalupian. 1) The long unknown stratigraphic relationship was documented for the first time between the Yabeina-dominant interval and the overlying Lepidolina-dominant one within a single limestone unit. 2) The occurrence of Lepidolina cf. kumaensis Kanmera, the unique last runner of large-tested fusuine, was detected for the first time in mid-oceanic paleo-atoll limestones. 3) With respect to the northbound migration history of the paleo-seamount capped by the Iwato Formation, the development of the two coeval fusuline biogeographic territories in the low-latitude Panthalassa, i.e., the Yabeina territory on the south and the Lepidolina territory on the north, was confirmed. 4) The paleo-latitude of the biogeographic boundary between the Yabeina and Lepidolina territories is constrained around 12° in the southern hemisphere on the basis of the latest geomagnetic data from the same limestone. This new approach utilizing biostratigraphy on ancient migrating seamounts coupled with geomagnetic paleo-latitude data is applicable to other cases in different time-space co-ordinates and of other fossil groups for constraining position of ancient biogeographic boundaries within lost oceanic domains of deep past. [Copyright &y& Elsevier]

Abstract: Diffusion and sorption behaviors of cationic Cs+, anionic I− and neutral HTO in samples of the Wakkanai Formation from the Horonobe underground research laboratory (URL), Japan, were investigated as a function of ionic strength (I) of synthetic groundwater by through-diffusion and batch sorption experiments and mechanistic modeling. The effective diffusivities (D e) measured by through-diffusion experiments showed cation excess and anion exclusion effects, which were strongly dependent on I; D e for Cs+ decreased as I increased, D e for I− showed the opposite dependency and D e for HTO showed no dependence. The sorption of Cs+ measured by through-diffusion and batch sorption experiments were described by Freundlich isotherms with consistent parameters and decreased with I as a result of competitive ion exchange. Diffusion and sorption behaviors were interpreted by assuming the clay components of illite and smectite control diffusion and sorption mechanisms. The component additive (CA) sorption model, which includes illite and smectite contents and their ion exchange constants, provided a reasonable account of the Cs+ sorption trends measured as functions of I and Cs concentration. The diffusion model was developed by coupling the electrical double layer (EDL) model, describing the change of ionic concentrations (cation excess and anion deficit) and viscoelectric effects caused by electrostatic interaction at negatively charged clay surfaces, and a simplified pore model assuming one type of pore shape and includes their size distribution. When averaging the electrostatic effects by using the pore surface area distribution, the model could predict the cation excess and anion exclusion effects, and its dependence on I reasonably well. This result implies the nanoscale pores dominating the pore surface area can strongly impact on ionic diffusion in argillaceous rocks. The clay-based modeling approach described here provides a useful tool to predict ionic diffusion and sorption in argillaceous rocks. [Copyright &y& Elsevier]

Abstract: An integrated magnetobiochronology of the Miyazaki Pliocene–Pleistocene succession in the Miyazaki area, southwest Japan, was established using planktic foraminiferal and calcareous nannofossil biostratigraphy together with paleomagnetic data. The upper Miyazaki succession in the northern Miyazaki region can be divided into the Takanabe, Hisamine (redefined), and Higoyashiki (new) Formations, in ascending order. A depositional hiatus between the Hisamine Formation and the Takanabe and/or older formations was also identified based on integrated magnetobiostratigraphy from five sections including the Nagatani River (NGT) section through the uppermost Miyazaki succession. The hiatus, herein called the Hisamine unconformity, is equivalent to the Kurotaki unconformity between the Miura and Kazusa groups of the Boso Peninsula in central Japan. The depositional hiatus recognised in the lower Pleistocene of Pacific coastal areas in southwestern and central Japan may have resulted from tectonic activity associated with a change in the subduction direction of the Philippine Sea plate, which commenced prior to ca. 2.2Ma. The youngest unit just below the hiatus is the upper part of the Takanabe Formation in the NGT section. The NGT section represents the continuous Late Pliocene to earliest Pleistocene sequence including the Gauss/Matuyama boundary and is here proposed as the type section for the Pliocene/Pleistocene boundary in Japan, which the IUGS ratified as the base of the Gelasian in 2009. [ABSTRACT FROM AUTHOR]

The Yezo Group has a wide longitudinal distribution across Hokkaido, northern Japan. It represents a Cretaceous (Early Aptian-Late Maastrichtian) and Late Paleocene forearc basin-fill along the eastern margin of the paleo-Asian continent. In the Nakagawa area of northern Hokkaido, the uppermost part of the Yezo Group consists of the Hakobuchi Formation. Along the western margin of the Yezo basin, 24 sedimentary facies (F) represent 6 facies associations (FA), suggesting prevailing storm-dominated inner shelf to shoreface environments, subordinately associated with shoreface sand ridges, outer shelf, estuary and fluvial environments. The stacking patterns, thickness and facies trends of these associations allow the discrimination of six depositional sequences (DS). Inoceramids Sphenoceramus schmidti and Inoceramus balticus, and the ammonite Metaplacenticeras subtilistriatum, provide late Early to Late Campanian age constraints to this approximately 370-m thick final stage of deposition and uplift of the Yezo forearc basin. Six shallow-marine to subordinately non-marine sandstone-dominated depositional sequences include four 10 to 110-m thick upward-coarsening regressive successions (FS1), occasionally associated with thin, less than 10-m thick, upward-fining transgressive successions (FS2). The lower DS1-3, middle DS4-5 and upper DS6 represent three depositional sequential sets (DSS1-3). These eastward prograding and westward retrograding recurring shallow-marine depositional systems may reflect third- and fourth-order relative sealevel changes, in terms of sequence stratigraphy. [ABSTRACT FROM AUTHOR]

Abstract: Plio-Pleistocene epithermal quartz veins in southern Kyushu, Japan, include gold deposits. The coherent trend of the ore veins suggests tectonic control for their formation. However, the stress regime during the formation has been controversial. To solve this problem, we improved existing methods for inferring paleostresses from vein orientations. It was assumed that veins making a cluster were formed intermittently from thermal fluids with various pressures. The present method determines stress ratio and stress axes with 95% confidence regions. The method was applied to mid Pliocene quartz veins cropping out at Hashima, southwestern Kyushu. We obtained a normal-faulting regime of stress with the trend of sigma3 at 167° ± 10° and the stress ratio at 0.20 + 0.13/−0.09. The low stress ratio and the lack of slickenlines and slickenfibers on vein walls suggest that the host rock was subject to a small differential stress, i.e., a weak tectonic stress, when the veins were formed. [ABSTRACT FROM AUTHOR]

Abstract: Temporal and spatial variations in concentrations of particle-associated polycyclic aromatic hydrocarbons (PAHs) and their nitrated and oxygenated derivatives (nitro-PAHs and oxy-PAHs) were investigated to assess the influence of secondary formation on atmospheric occurrences of oxy-PAHs associated with particulate matter in downtown Tokyo, Japan. The daily variation in concentration of 1,8-naphthalic anhydride (1,8-NA) in summer 2007 was similar to that for 2-nitrofluoranthene (2-NF), a representative secondary formed nitro-PAH, while the variation for benzanthrone (BA) was similar to PAHs. In addition, the concentrations of polycyclic aromatic compounds (PACs) associated with airborne particulate matter decreased in the order of PAHs>BA>9-fluorenone (9-FO) or 9,10-anthraquinone (9,10-AQ)>1,8-NA with an increase in distance from the roadside, whereas 2-NF was constant. These results suggest that a considerable fraction of some oxy-PAHs such as 1,8-NA associated with airborne particulate matter in downtown Tokyo originates from atmospheric secondary formation. [Copyright &y& Elsevier]

Abstract: The Kurotaki Unconformity is located in the Boso Peninsula between the subduction zone in the Pacific Plate and the Philippine Sea Plate. The underlying stratum (Miura Group) and overlying stratum (Kazusa Group) bordering the Kurotaki Unconformity are greatly different with respect to geologic structure and age. The influence of the Pacific Plate is reflected in the Kazusa Group, and that of the Philippine Sea Plate in the Miura Group. Thus, the Kurotaki Unconformity gives a geological constraint on tectonic conditions around the Japanese Islands. This study has clarified of the formation age of the Kurotaki Unconformity based on tephrochronology. The age of the unconformity is ca. 3.0–2.8 Ma. The formation age of the unconformity is specified based on tephrochronology. Common and widespread tephra layers were found in strata bordering the unconformity. The formation of the regional Kurotaki Unconformity indicates a widespread event in the vicinity of the newly designated Pliocene–Pleistocene boundary in the Japanese Islands. [Copyright &y& Elsevier]

Across-shelf variations in thickness, grain size, and frequency of sandstone beds in a transgressive outer-shelf succession were investigated from the Middle Pleistocene (ca. 0.7Ma) Kakinokidai Formation on the Boso Peninsula, Japan. The transgressive deposits are generally muddy and contain slumps and slump scars. The intercalated sandstone beds are interpreted to have been formed from turbidity currents as a response to erosion and resuspension of sandridge-complex deposits in the southwestern upslope area during storm events. Mapping of volcanic ash beds and a transgressive surface in the base of the formation permits detailed bed-by-bed correlation of the outer-shelf sandstone beds. Although, overall, thickness, grain size, and frequency of sandstone beds decrease in the downslope direction, some sandstone beds locally thin out and coarsen in association with slump scars in the surrounding muddy deposits. These sandstone beds subsequently thicken and fine, and finally thin out in the farther downslope area. In addition to the local thinning of sandstone beds, the frequency of sandstone beds first decreases and then increases in the farther offshore direction. From this evidence, we concluded that these non-uniform patterns of across-outer-shelf variations in thickness, grain size, and frequency of sandstone beds were caused by the local increases in flow speeds and subsequent expansion and reduced speeds of turbidity currents, along with a local increase in the seafloor gradient that was induced by the development of slump scars in the transgressive outer-shelf floor. These physiographic features in the outer shelf are interpreted not to have permitted monotonous downslope thinning and fining of sandstone beds, compared with the bed-shape models of depletive turbidity currents and with the proximality trend of shelf sandstones from modern and ancient highstand-stage shelf systems. [Copyright &y& Elsevier]

We investigated the sequence variation in the mitochondrial cytochrome c oxidase subunit 1 (mtCOI) gene and the nuclear ribosomal internal transcribed spacers (ncITS) of the calanoid copepod Acanthodiaptomus pacificus in Japan. A. pacificus individuals were divided into three divergent mtCOI lineages (mt-A, -B and -C). mt-A was distributed in the northernmost part of Japan, from Hokkaido to the northern part of Honshu Island, whereas mt-C was the southernmost lineage, distributed from central Honshu to Shikoku and Kyushu Islands. mt-B was distributed between these former two lineages, resulting in parapatry with mt-C and mt-A. In all lineages, 80% of the localities were fixed for a single haplotype, and different localities tended to have different haplotypes. The degree of genetic differentiation among these lineages (15–22%) was at an interspecific level, according to the criteria of the DNA barcode technique. However, the topology of ncITS was not congruent with that of mtCOI, as the reciprocal monophyly was not observed within mt-B and mt-C. Therefore, we merged them into the Southern Lineage and separated it from the Northern Lineage (i.e. mt-A). Evidence of introgression was found within the Southern Lineage, while gene flow was not observed between the Northern and Southern Lineages, suggesting that A. pacificus is a cryptic species complex. We also argue that genetic differentiations of A. pacificus in Japan may reflect the history of separation, transgression and regression of the landmass during the formation of current Japanese Archipelago. [ABSTRACT FROM AUTHOR]

Abstract: There are a few marine intercalations in the upper Mesozoic nonmarine deposits in the eastern part of the Asian continent, including the Tetori area, Japan, and the eastern part of the Heilongjian Province, China. Therefore, it is possible to apply international marine stage names roughly for these nonmarine deposits. We can then discuss the changes of terrestrial environments in East Asia and their accompanying terrestrial and freshwater biotas. To date, two marine transgressions have been recognized in the Tetori Group, Japan. One is of the stage from Callovian to Oxfordian, and the other is from Tithonian to Berriasian. Recently a new marine biota was discovered from the Inagoe Formation of the Tetori Group. Four species of ammonites and 13 species of bivalves from the biota are described herein. The presence of Psedothurmannia aff. baleare, Phyllopachyceras infundibulum, and Acrioceras (Paraspinoceras) sp. suggests that the Inagoe Formation can be assigned to Hauterivian to Barremian. Those data indicate that the third marine transgression is represented in the Tetori Group. In the eastern part of the Heilongjian Province, China, two marine transgressions, the first from late Oxfordian to Volgian (=Tithonian to early Berriasian) and the second from Barremian to Aptian, are recognized. Therefore, those marine transgressions in China correspond to those in the Tetori area, Japan. The presence of common marine bivalve species and related ammonite species suggests that the eastern part of the Heilongjiang Province of China and the Tetori area of Japan occupied the same faunal province during Hauterivian to Barremian time. These faunal compositions are different from those of the areas in the southwest of Japan influenced by currents from low latitudes. This supports the idea that a peninsula of land was present between both the Tetori area and areas in southwest of Japan. Thus, both areas of the eastern part of the Heilongjian Province of China and the Tetori area of Japan, were influenced by current from the high latitude. [Copyright &y& Elsevier]

Abstract: Seven Barremian ammonoid species and two Aptian species from the Choshi Group, Japan, are described here. Among the Barremian forms, new species of Holcodiscus and Pulchellia are proposed. Furthermore, three Albian ammonoid species are also described as derived Cretaceous fossils mainly from the Miocene Naarai Formation. The Choshi fauna shows a high similarity to that of the Mediterranean region of the Tethyan realm (Obata and Matsukawa, 2007). All the described species of ammonoids from the Choshi Peninsula are listed and their geological ages are discussed. [Copyright &y& Elsevier]

Abstract: Saline type groundwaters data in the Mobara area (a marine based argillaceous rock) located in the well-known “South Kanto gas field” in Japan were investigated by JNC [1] JNC (Japan Nuclear Cycle Development Institute) was merged in October 2005 with the Japan Atomic Energy Research Institute (JAERI) to form the Japan Atomic Energy Agency (JAEA). 1 as part of a natural analogue study. Most groundwaters in the field were extracted from deep gas wells (e.g., 400–2000m below the surface), and the all data reported previously were sampled at the wellhead, where physico-chemical parameters (e.g., temperature, pH, Eh etc.) were also measured. In such cases, particular attention should be paid to whether the measured and/or analyzed results are consistent with the chemical and physical conditions in the in situ geological formation because air contamination, the temperature and pressure changes during sampling can affect the groundwater chemistry. The present study shows a test case to estimate the in situ groundwater chemistry in argillaceous rock of the Mobara area using geochemical model calculations. Results from thermodynamic interpretation of groundwater chemistry using the measured pH and Eh of groundwater sampled at wellhead (e.g., pH=7.86, Eh=−50mV) indicate that the groundwaters are supersaturated with respect to calcite (e.g., the saturation index; SI is 1.14). Calcite is known to equilibrate relatively quickly with aqueous solutions at low temperatures and this mineral is present in the Otadai formation, however. Therefore the values greater than 0 for SI of calcite may be due to errors in the pH measurement. Also the measured Eh is relatively oxidizing value which may be inconsistent with the in situ geochemical conditions (e.g., pyrite and siderite coexist, CH4(g) dominates in the groundwaters). Thus such Eh value may be disturbed by contact of the samples with atmospheric oxygen and other effects like degassing. Errors in the pH measurement might be caused by degassing during sampling of groundwaters. As a test case to estimate the groundwater considering such degassing effect, we first assume that the in situ groundwaters are saturated with respect to calcite. A back-titration geochemical model is then used to simulate the addition of CO2(g). Regarding the redox conditions of groundwater, we also assume that pyrite–siderite equilibrium controls the Eh of Mobara groundwaters considering the mineralogy identified in the Otadai formation. The assumed equilibrium between pyrite and siderite implies a fixed value of at a given temperature and pH. A back-titration of trace levels H2S(g) is also applied to estimate the possible effect of the in situ Eh and pH of groundwaters. The calculated result shows that pH is about 6.7 and Eh is about −190mV, respectively. The estimated pH value for the in situ groundwater is about 1 unit lower than the measured pH value at the surface and the in situ redox potential is significantly lower than Eh value measured in surface sample. Based on a preliminary assessment of mineral-water equilibria using the mineral stability relations in the CaO–MgO–Al2O3–SiO2–H2O system, the estimated in situ groundwater composition is more consistent with the mineralogy of the Otadai formation than the measured groundwater composition. However, further consideration (e.g., detail mineralogical investigation, reliable and consistent thermodynamic data with site mineralogy) would be needed to check the reliability of estimation technique. [Copyright &y& Elsevier]

Abstract: A hydrogeochemical investigation is being carried out as part of the Horonobe underground research laboratory (URL) project in Japan. The main aims are to: (1) investigate an actual example of a geological environment in a sedimentary rock formation in Japan; and (2) to confirm the reliability of generic technologies that may in future be applied during the geological disposal of high level radioactive waste. The main rock formations being characterized are the marine Wakkanai and Koetoi Formations (Miocene to Pliocene), consisting dominantly of siliceous shales (porcelanites) and diatomaceous shales respectively. These formations are located within the Tempoku Basin, within a back-arc tectonic setting. Rock sequences of this kind occur widely in Japan and throughout the northern Pacific region. However, prior to the present study, there was relatively little information concerning the processes controlling in situ chemical conditions and groundwater flow in such settings. Chemical data was obtained for both pumped waters and squeezed porewaters in order to characterize the hydrogeochemistry of these argillaceous rock formations. The in situ chemical conditions, residence time of the groundwaters and the evolution processes of the groundwaters were investigated. Generally, at each locality studied, shallower groundwaters are fresh and have Na–HCO3 dominated chemistry. Deeper groundwaters are saline (TDS up to about 22,000mg/l) and have Na–Cl dominated chemistry. However, lateral gradients in salinity are also recognized, with salinity contours in the Na–Cl dominated saline water (having TDS>10,000mg/l) probably varying in elevation by at least 250m. Further investigations are required to confirm the origins of the groundwater salinity, but the Na–Cl dominated groundwater chemistry is provisionally explained as a consequence of the dilution of fossil seawater, accompanied by diagenetic water–rock reactions. The vertical and lateral salinity gradients can potentially be used to test the validity of coupled groundwater flow models. A conceptual model is tentatively suggested in which the spatial distribution and frequency of fractures helps to control the spatial distribution of groundwater salinity. Future investigations will clarify the timing of flow, the flow directions and the characteristics of the flow paths. [Copyright &y& Elsevier]

A seismic waveform inversion algorithm is proposed for the estimation of elastic soil properties using low amplitude, downhole array recordings. Based on a global optimization scheme in the wavelet domain, complemented by a local least-square's fit operator in the frequency domain, the hybrid scheme can efficiently identify the optimal solution vicinity in the stochastic search space, whereas the best-fit model detection is substantially accelerated through the local deterministic inversion. Results presented for selected aftershocks of the M w 7.0 Sanriku-Minami earthquake in Japan, recorded by the Kik-Net Strong Motion Network, illustrate robustness of the impedance structure estimation. By contrast, the attenuation structure is shown to be sensitive to the frequency content of seismic input data, attributed to the deterministic description of the continuum in the forward model that cannot simulate late arrivals of multiple-scattered energy. Sensitivity analyses illustrate that for the same forward model, results can be substantially different based on the definition of the objective function. It is concluded that even for engineering purposes, inversion should aim to decouple intrinsic and scattering attenuation mechanisms. [ABSTRACT FROM AUTHOR]

The article describes the Permian ammonoids Prostacheocers and Perrinites from the southern Kitakami Massif, Northeast Japan. The stratigraphic and biogeographic significance of these ammonoids are also discussed. In the course of the geologic survey of the Permian, two ammonoid fossils from the lower part of the Sotokawame Formation were collected. These provided a basis for stratigraphic correlation.