The eastern segment of the Inagoe Fault in the Furukawa Fault Zone, northern Gifu Prefecture, is thought to be active based on the discovery of active fault outcrops and geomorphologic evidence. Although the fault trace is thought to extend westward to the Kurigatanigawa area along the western segment of the fault, direct geologic evidence of fault activity there has not been reported. This study describes a newly discovered active fault outcrop along the western segment of the Inagoe fault and assesses fault activity on this segment. The outcrop is located on the trace of the Inagoe Fault and has a 5 m-wide fault gouge or breccia zone. The composite planar fabric in the fault gouge zone shows a dextral sense of shear, consistent with the sense of movement of the fault inferred from stream offsets. Unconsolidated sand and gravel layers, which were originally deposited above the fault zone, are also sandwiched within the fault zone. The major axes of gravel clasts adjacent to the fault gouge are vertical, and striations are found on their surfaces. Radiocarbon dating of a soil sample in the sand and gravel layer yields an age of AD 1521-1658, suggesting that an earthquake occurred on the western segment of the Inagoe Fault after this time. These observations suggest that (1) the fault outcrop corresponds to the core of the Inagoe Fault, (2) an overlying sand and gravel layer fell into crack and was subsequently deformed by movement on the fault, and (3) the western segment of the Inagoe Fault might have ruptured during one of the four historical earthquakes known to have occurred in northern Gifu Prefecture over the past few hundred years.

The Tatenosawa Sandstone Member of the Upper Jurassic Nakanosawa Formation (part of the Somanakamura Group) is a series of regressive sandy deposits that lies above a basal transgressive lag facies that was deposited on a wave-ravinement surface overlying the sandy, fluvial Tochikubo Formation. The Tatenosawa Sandstone Member shows a shallowing-upward facies succession, from open shallow marine to inner bay lagoon sedimentary environments. The member was formed by the repeated progradation of siliciclastic depositional systems during a slow relative sea-level rise with several small oscillations. The Koike Limestone Member formed a carbonate platform several kilometers wide (E-W) and 10 km long (N-S) as carbonate barrier-lagoon systems were established after siliciclastic sediment supply ceased. Five fining-upward facies successions (< a dozen m thick) can be identified across the entire study area. They were formed by five regressions and transgressions driven by small-scale relative sea-level change, each of which caused the sedimentary environment to change from foreshoal through oncoid shoal and backshoal to lagoon environments. We suggest that the deposition of the Nakanosawa Formation reflects third-order sea-level cycles during the second-order highstand from the Kimmeridgian to the early Tithonian.

A better understanding of the response of the Antarctic ice sheet (AIS) to climate change is important because it is thought to contribute significantly to future sea-level rise. Satellite and geodetic observations are powerful tools for capturing relatively short-term variability in the AIS. However, these observations are not enough for understanding the mechanism of the changes in the AIS because it may change more dynamically over longer time scales; therefore, it is essential to reconstruct the long-term variability in the AIS (a few decades-hundreds of thousand years). Sea-level records reconstructed from geological records and models of glacial isostatic adjustment (GIA) are keys to reconstructing the AIS changes for longer time scales. This paper summarizes the published data on sea-level change and GIA modeling in East Antarctica and discusses the potential future directions of this research topic.

There is an amazing array of concretions throughout the sedimentary record of Earth, and now iron oxide examples (“blueberries”) recognized in several regions of Mars. Two questions address the current state of knowledge on nodular cemented mineral masses as well as coloration patterns. Collectively the authigenic cements and patterns chronicle past diagenetic conditions, particularly in clastic rocks.

What do we know? Concretions are cemented mineral masses that occur in many sizes, spanning three orders of magnitude (mm, cm, and m scales). Spheroidal forms are most common, as an minimum free stage dominated by diffusive processes. There are multiple cement mineralogies, sometimes even within single concretions, reflecting different water compositions in open systems. Other concretionary geometries are affected by primary textures such as bedding, grain size, and porosity/permeability, or later textures such as fractures, joints, and faults. Iron cycling is readily apparent where visual coloration patterns indicate histories of early iron reddening, secondary bleaching (removal of iron), and iron replacement or reprecipitation. Interfingering colors may indicate a possible interface of immiscible fluids.

What are the remaining challenges? There are many aspects of concretion diagenesis that are still yet to be deciphered. Non-unique pathways or processes may produce similar-looking end products. Thus, it can be difficult to determine exact histories, as well as the fluid compositions and environmental conditions that initiate concretion formation, particularly if an obvious nucleus is lacking. Microbial life may enhance nucleation and precipitation, and geochemical gradients are potential places to search for biosignatures. Timing and events are mostly relative relationships in these open systems, but newer developments in U-Th/He dating may provide age constraints for iron oxide cements. Continued explorations, field studies, modeling approaches, analytical advances, and instrument precision will enlighten our understanding on the diagenetic histories of both Earth and Mars.

Basaltic rocks with N-MORB features of the Shimokawa ophiolite in the northern Hidaka belt, Hokkaido, generally show poor vesiculation. Some of dolerites are vesiculated up to 10% that are exclusively found within thick sills (> 10 m) interlayered between sediments. The thick dolerite sill about 22 m thick was studied in detail. The chilled margin is not vesiculated, but the inside of the sill is vesiculated from 5-10%, indicating that the magma was not vesiculated at the intrusion.

Albite -K-feldspar veins about 2 mm wide are found within the dolerite sill. The veins are irregularly bounded and cut by other veins, and contain relatively large rounded vesicles. Therefore, the veins were formed before the solidification of the sill. The bulk composition of the vein shows trachytic composition. It’s difficult that trachyte melts are produced by fractional crystallization of MORB magma. Mineral compositions of the veins show that they were crystallized below solvus temperature. The bulk composition of dolerite is higher in K₂O and Rb than poorly vesicularity basalt.

The sediments are silicified along the contact to the dolerite sills. LIL elements are highly depleted, while Na₂O contents are enriched in the silicified sediments. Thus, intrusion of magmas into the thickly accumulated soft sediments resulted in induration of the sediments from which the trapped seawater (H₂O and NaCl), LIL elements and CO₂ were expelled due to the dissolution of organic carbon. The expelled Na₂O partly precipitated albite in the silicified part. Thus, vast fluids rich in Na₂O and K₂O, caused by an intrusion of magmas into soft sediments, were discharged into the magmas and resulted in vesiculation of the magmas. Finally, the fluids were solidified as the albite -K-feldspar vein.

The Hiwadatoge Formation in northwestern Shikoku, Southwest Japan, represents the oldest strata overlying the Sambagawa metamorphic rocks and is, therefore, often used to constrain the timing of the denudation of the Sambagawa metamorphic rocks. Despite its significance, previous studies on the formation are limited, and even the geological relationship between the formation and the Sambagawa metamorphic rocks has yet to be described in detail. To rectify this, we conducted geological mapping and detrital zircon U-Pb dating. The Hiwadatoge Formation is >100 m thick and composed of pebble to granule conglomerate and sandstone, which have local calcareous matrices. The formation is interpreted as southward-prograding shallow marine fan delta deposits. Most of the clasts in the formation were derived from the Sambagawa metamorphic rocks, but igneous rocks of the Ryoke, San-yo, and San-in belts were probably also sources of clastic grains. In addition to foraminifers and dinoflagellate cysts from previous studies, fossil bivalves and detrital zircon U-Pb ages in our study indicate that the formation was deposited during the early Lutetian (middle Eocene). The formation nonconformably overlies the Sambagawa metamorphic rocks and is unconformably overlain by the Kuma Group (and locally by the Ishizuchi Group). Therefore, the Sambagawa metamorphic rocks had been exposed and started eroding by the earliest middle Eocene, at least in the Shikoku region.

Glendonite is a calcite pseudomorph after ikaite and is found in sedimentary rocks worldwide. Glendonite concretions are spherical to ellipsoidal carbonate concretions containing glendonite at their center. Glendonites and glendonite concretions have been widely used as indicators of low temperatures because ikaite, a precursor of glendonite, is stable only in low-temperature environments. The process that forms glendonite concretions means that they are also potential indicators of the chemical environments of sediment porewaters. However, the physicochemical conditions required for the formation of ikaite in sediments remain poorly constrained. As the conditions of formation of both ikaite in modern sediments and glendonite in sedimentary rocks are clarified, the use of glendonite and glendonite concretions as environmental indicators will increase.

Miocene sedimentary sequences are distributed widely in Oki Dogo Island, Shimane Prefecture, Southwest Japan. Among them, the lowermost part of the Kumi Formation recorded a transition from freshwater to marine environments associated with the opening of the Japan Sea. We analyzed radiolarian fossils collected from the Kumi Formation in its type locality. We identified Eucyrtidium inflatum, Subzone and Lychnocanoma magnacornuta Zone in the upper part of the Kumi Formation and the Melittosphaera magnaporulosa Zone in the lower part. In addition, the lowe part of theKumi Formation yielded the P-C assemblage composed of two species: Pentactinosphaera hokurikuensis and Cyrtocapsella tetrapera. This assemblage is unique to the earliest stage of the Japan Sea opening because it was identified immediately above non-marine sedimentary rocks. In contrast to Miocene in coastal area of Japan Sea, the specific assemblage is considered to be the most similar to that of Okushiri Island based on the composition of siliceous microfossils.

We investigated the hydraulic and mechanical properties of spherical calcium carbonate concretions and their surrounding matrices in a Neogene accretionary deposit in the Hayama Group (Kanagawa prefecture) and a brackish to marine formation in the Mizunami Group. The concretions in both formations have lower permeabilities and porosities and greater hardness than the surrounding host rocks. Although the concretions in both formations were formed in different depositional environments, they hardened a short time after the death of a living organism. This means that they can be considered stable over long periods and would not be significantly affected by subsequent deformation and tectonic events. This property is useful for engineering applications, as it would yield a long-lasting seal.

We present a diatom assemblage from two carbonate concretions hosting ammonite specimens from the Saku Formation (upper Turonian, lower Upper Cretaceous) in the Teshio-Nakagawa area, Hokkaido, northern Japan. Hemiaulus, Triceratium, and Costopyxis are the major taxa in the assemblage, and they are typical of upper Upper Cretaceous (Campanian-Maastrichtian) deposits. In contrast, the primitive cylindrical diatoms that are found mainly in Albian and Cenomanian deposits are largely absent, except for Gladius sp.

Previous records of mid-Cretaceous diatoms are rare, and our study documents the first well-preserved specimens from late Turonian deposits that have been reliably dated by refined molluscan biostratigraphy. We confirm that mid-Cretaceous diatoms overturned dramatically during the Cenomanian-to-Turonian interval, at the onset of the extreme paleoceanographic crisis known as the Ocean Anoxic Event 2.

A rapid transgression occurred at the end of the early Miocene in the eastern San’in region, Southwest Japan, owing to tectonic subsidence associated with the back-arc rifting that lead to the opening of the Sea of Japan. This study aims to provide new constraints on the date of initiation of the transgression in this region. The deposition of the early-middle Miocene Iwami Formation was contemporaneous with the transgression. The lower part of the formation in the Miyanoshita area, Tottori Prefecture, is composed of terrestrial deposits covered by brackish-water mudstones. We dated a tuff bed intercalated with the mudstone. The ²³⁸U-²⁰⁶Pb ages of zircon grains separated from the tuff were measured using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and a weighted mean age of 17.4±0.2 Ma (95% confidence interval, MSWD = 3.7, n = 27) was obtained after excluding a Cretaceous age from one grain. This age is older than that indicated by other evidence of marine environments in the eastern San’in region. The lithofacies of the upper lower Miocene strata suggest that the Miyanoshita area was an alluvial lowland just before the rapid transgression. Therefore, we conclude that the Miyanoshita area was submerged ~0.4 My earlier than other areas because of its paleogeography.

A new specimen of a fossil tooth of the Suidae (Mammalia, Artiodactyla) discovered in the upper Miocene Oiso Formation (ca. 8.29-5.57 Ma) of the Miura Group, Kanagawa Prefecture, Japan, is described. The tooth is left m3, and its hypoconulid has broken away. It is bunodont, low-crowned, and moderately to heavily worn. The m3 has the typical lower molar morphology of a medium-sized suid, with some furrows on the cusps. The part of the tooth containing the first two lobes is relatively elongated, similar to that of m3 of the Suinae. It is more elongated than that of m3 of the Asian Tetraconodontinae. Based on its size and observable morphology, this m3 is most comparable to that of Propotamochoerus hyotherioides (Suinae). This discovery reinforces the hypothesis that the Oiso Formation was deposited in the Honshu Arc, rather than the Paleo-Izu Arc. Only seven (five Miocene and two Pliocene) suid specimens have been reported from the Neogene of Japan to date.

This paper introduces two early-stage engineering applications inspired by concretion formation, a naturally occurring elemental and molecular concentration process. First, the precipitation of iron oxide from highly acidic wastewater using cement clinker and its applications to channel control were investigated. Blocking of channels by iron oxide precipitating around the clinker was confirmed using a column test. Second, the production of “Calcium carbonate concrete” using concrete waste and CO₂ in the air was investigated, based on the fact that calcium carbonate is the binding material in calcium carbonate concretions. Understanding the natural mechanism of concretion formation is not only a fascinating topic from a scientific perspective, it also has potential engineering applications.

Hotokegaura on the Shimokita Peninsula, northern Japan, is one of the most popular geosites in the Shimokita Geopark. The unique coastal landscape consists of numerous pinnacles of pale green lapilli tuff, which is often referred to as a typical example of Miocene “green tuff” that represents the intense volcanism associated with back-arc spreading of the Sea of Japan. However, little geological and chronological data have been collected since geological mapping was conducted in the 1960-70s. As a part of a scientific research project funded by the Shimokita Geopark, we measured the zircon U-Pb ages of two tuff samples from the Hotokegaura area and obtained ²³⁸U-²⁰⁶Pb ages of 4.2-4.1 Ma. These Pliocene ages challenge the previous stratigraphic assignment of the Hotokegaura tuff beds to the Miocene Hinokigawa Formation and suggest that a re-examination of the regional stratigraphy is necessary.

A fossil specimen of Anthracokeryx naduongensis (Mammalia, Artiodactyla, Anthracotheriidae, Microbunodontinae) discovered in the middle/upper Eocene Na Duong Formation at Na Duong Coal Mine in northeastern Vietnam is described. The specimen is a left mandibular fragment preserving p3-m3. It is characterized by an association of features that is observed in A. naduongensis, including a small size relative to most of other anthracotheriids, bunodont to bunoselenodont dentition, weak cingula, and a hypolophid on the lower molars. This specimen illustrates the precise morphology of m2-m3 of A. naduongensis from the type locality.

Numerous carbonate concretion samples were collected during dredging around Nagoya Port in the 1960s. Most of the samples contained biological remains, including crabs, sea urchins, and bivalves, which formed their nuclei. In this study, the radiocarbon (¹⁴C) ages of the shells of the biological remains inside the concretions, as well as of the concretions themselves, were determined. Based on the metabolic carbon ratios of the bivalvia and sea urchin shells, which were calculated using δ¹³C values, the ¹⁴C ages of the shells and those of the metabolic carbon were estimated to be 7,350-7,050 cal BP and 9,680-9,430 cal BP, respectively. The ¹⁴C ages of the carbonate concretions were older than those of the shells due to the addition of metabolic carbon with older ages to the carbon of the concretion. The corrected age after removal of the old carbon was estimated to be 7,530-7,270 cal BP. The near-identical corrected ages of the shells and concretions indicate that the carbonate concretions in the Nagoya Port area formed rapidly after the death of the organisms, which is consistent with morphological evidence of rapid concretion formation in the sediment.

The depositional age of the E-W-trending Ryujin Complex in the Shimanto Accretionary Prism on the Kii Peninsula has been studied mainly in the western and central parts of the complex, and no geochronological data have been reported from the eastern part. Here we present U-Pb and fission-track (FT) ages of zircon grains from felsic tuff in the Sohgawa Unit in the eastern part of the complex. The weighted mean U-Pb age is 68.1±0.4_(2σ) Ma, which indicates deposition during the late Maastrichtian and is similar to ages obtained for the western and central parts of the complex using radiometric data and radiolarian fossils. However, the tuff yields a zircon FT age of 13.3±1.6_(2σ) Ma, which is similar to the radiometric ages of the Middle Miocene igneous rocks exposed around the study area, suggesting that the FT age has been reset by heat from the igneous rocks.

The Nedamo Belt in the Kitakami Massif, NE Japan, contains early Carboniferous and Early Triassic accretionary complexes. Tectonic blocks containing plutonic rocks, ultramafic rocks and high-P/T schists occur in these complexes and characterize the Nedamo Belt. The plutonic rocks comprise hornblende gabbro and quartz diorite, and they have been identified at more than 50 localities. U-Pb dating of zircon from the quartz diorite using inductively coupled plasma-mass spectrometry yields an Early Ordovician age of ca. 480 Ma. Based on similarities in lithofacies and age, the plutonic rocks are correlative to the Kagura Igneous Rocks of one of the basement units in the South Kitakami Belt. This correlation may help in deducing the mechanism (e.g., large sinistral strike-slip fault) of emplacement of the tectonic blocks into the accretionary complexes of the Nedamo Belt.

The upper Miocene to Pleistocene Shimajiri Group, composed mainly of siltstone and sandstone, occurs on some of the Ryukyu Islands in southwestern Japan. This group is thought to have been deposited in a shelf-slope to fore-arc basin setting before the accumulation of Pleistocene coral reef deposits (Ryukyu Group). We investigated the calcareous nannofossil biostratigraphy of the Shimajiri Group in the Offshore Okinawa 1-x well, drilled near the northeastern margin of the Okinawa-Miyako Submarine Plateau, Ryukyu Islands. A sample from 280 m, at the base of Ryukyu Group, contains Gephyrocapsa parralella, which first occurred at 0.987 Ma. Discoaster quinqueramus and D. berggrenii, which define both the top and bottom of the calcareous nannofossil zone NN11, are found throughout the Shimajiri Group, consistent with a late Miocene age between 8.10 Ma and 5.53 Ma. A large sedimentary gap between the Shimajiri and Ryukyu groups suggests that part of the Okinawa-Miyako Submarine Plateau may have been above sea level during the early Pliocene, implying deposition of the Shimajiri Group here was completed earlier than in other regions. This study provides key constraints on the Cenozoic geological history and phylogeography of the Ryukyu Islands.

This paper describes the mode of occurrence of the Rendaiji Gravel Bed that is newly exposed in the quarry of Rendaiji, Yuzawa City, Akita Prefecture. The bed is of unknown attribution, >10 m thick, and comprises 15 or more flow units. Constituent gravels characteristically contain kaolin minerals and lesser amounts of cristobalite and/or smectite, together with iron oxides and hydroxides formed by weathering of iron sulfides. Most of the gravels rich in kaolin minerals are plastically deformed, have lenticular or thin platy morphology, and are accompanied by sparse larger gravels of kaolin mineral-bearing tuffaceous rocks. Individual flow units are poorly sorted and non-stratified with a sharp base. In many cases, they show inverse grading in the basal part and finer-grained laminations in the uppermost part. Associated with minor cristobalite and/or smectite, kaolin minerals commonly replace volcanic glass shards. In addition, crossbedding and flame structures suggest a paleoflow from the southeast. The gravelly deposits are interpreted to have been settled from lahars that were derived from one of the geothermal areas in the Sanzugawa Caldera that have been active since 2 Ma. Lenticular and/or platy, plastically deformed gravels were likely concentrated and emplaced parallel to one another from viscous laminar flows.

Spherical iron-oxide concretions are found in the Jurassic Navajo Sandstone in Utah, USA. Based on image analysis of more than a thousand concretions, we found that: (1) the spatial distribution resembles a random distribution, with deviation from the random distribution occurring as concretion clusters; (2) the spacing between concretions is much larger than the concretion sizes; (3) the width of the size distribution increases with increasing concretion size; and (4) the volume fraction of concretions is constant, irrespective of size. These characteristics can be explained by repeating cycles of CaCO₃ dissolution and precipitation, the precursor material of Fe-oxide concretions. In numerical simulations, the width of the size distribution did not depend on the input parameters, including pH and supersaturation.

The Early Cretaceous Oshima Orogeny in NE Japan was characterized by extensive magmatism and intense tectonic deformation, including folding before the late Aptian. However, the stress inversion of dike orientations in Jurassic and older accretion complexes in the Kitakami Mountains recently revealed an extensional setting during the mid Early Cretaceous. Unfortunately, it is difficult to evaluate the influence of the post-intrusion tilting of the dike attitudes, because the host of the dikes has complicated geologic structures. It is, accordingly, difficult to interpret the inversion result. Here, we inverted orientation data from quartz veins in the basement of the Upper Cretaceous formations that deposited shortly after the vein formation. As the data were collected near the base of the formations with dip angles smaller than ~20°, we could ignore the tilting of the veins to qualitatively interpret the extensional stresses that were determined by the inversion. The tectonostratigraphy and magmatic history of the northern Kitakami region suggest that the stresses were of the Aptian time. Thus, it was confirmed that the Kitakami region was subjected to extensional stress conditions. The stress change from compression to extension occurred around the Barremian-Aptian boundary.

The understanding of modern sediments and sedimentary processes has improved considerably in recent decades. In particular, studies have progressed from simply characterizing modern sediments to understanding modern depositional systems. Recent progress in modern sedimentology includes event-related deposits and their depositional processes. International and interdisciplinary science programs on material and carbon cycles in oceans and on stratal formation have contributed to our understanding of flood-related event deposits and their depositional processes. Rapid-response surveys after the 2011 Tohoku-oki earthquake and subsequent tsunami provided an opportunity to study event deposits and their depositional processes. The integration of geological sediment studies, field observations, laboratory experiments, and numerical simulations under international and multi-disciplinary frameworks is important for the further development of modern sedimentary studies.

The Moriya Formation in central Nagano Prefecture, Japan, records the paleoenvironment and crustal movement in central Hon-shu during the Miocene. The lower part of the formation consists of clastic sedimentary rocks, and the upper part comprises altered volcanic rocks. Fossil foraminifera indicate that the clastic sedimentary rocks were deposited during the period of the N8 planktonic foraminiferal zone (17.0-15.1 Ma). However, no previous studies have reported ages for the overlying volcanic rocks. Here we present zircon U-Pb ages for the uppermost volcanic member of the Moriya Formation. We obtained a weighted mean age of 15.5±0.2 _(2σ) Ma, indicating that Miocene volcanic activity started after 17.0 Ma and continued until ca. 15.5 Ma. This formation, including the upper volcanic rocks, can be correlated to the lower-middle Miocene Uchimura Formation, a lithostratigraphic division of a representative stratigraphic succession in the northern Fossa Magna region. The volcanic rocks of the Moriya Formation are older than most of the Shitara (Shidara) volcanic rocks (ca. 15-13 Ma) in Aichi Prefecture but may be coeval with andesitic-basaltic rocks exposed around the Aichi/Nagano prefectural boundary (the Tsugu volcanic rocks).

Towada Volcano is an active volcano located in the northern part of the Northeast Japan Arc. This study describes the stratigraphy, field characteristics and eruptive sequence of Eruptive Episode M, which occurred at 21 cal kyr BP during the caldera-forming stage. The proximal eruptive products consists of the Kumoi Pyroclastic Flow Deposits and Karatamazawa Pumice; the distal facies consists of the Maita Tephra (subdivided into the Maita 1 Pumice and Maita 2 Ash). The Karatamazawa Pumice and Maita Tephra are pyroclastic fall deposits probably derived from Plinian and phreatoplinian eruptions. All these deposits are composed of phenocryst-poor vesiculated rhyolite pumice. Their stratigraphic relationship remains unknown because they have not been observed in the same outcrop. The Kumoi Pyroclastic Flow Deposits and the Karatamazawa Pumice are estimated to be contemporaneous with the Maita 2 Ash based on the similarity of petrological features. During Eruptive Episode M, a Plinian eruption first formed the Maita 1 Pumice; shortly thereafter, intermittent phreatoplinian eruptions under the influence of lake water formed the Maita 2 Ash and Karatamazawa Pumice. During these eruptions, the eruption column partially collapsed and the resulting pyroclastic flows emplaced the Kumoi Pyroclastic Flow Deposits. The apparent and dense rock equivalent eruptive volumes of Eruptive Episode M are estimated to be 9.0 km³ and 2.8 km³, respectively.

The volcanic stratigraphy, geologic structure, petrography, and chemistry of the Abu Group were examined, along with its relationship with associated intrusive rocks, to investigate the geologic history of a Late Cretaceous caldera cluster in the Nagato-Hōhoku area of Yamaguchi Prefecture, Japan. The stratigraphy of the Abu Group in this area is divided into the lower Hōhoku and upper Nagato formations. The Hōhoku Formation is composed mainly of tuffaceous sedimentary rocks and is divided into the Awano Conglomerate and Sandstone, Hōzōyama Lapilli Tuff, Ōtōyama Tuff, and Asōgawa Shale and Tuff members. The Nagato Formation consists mainly of terrestrial volcaniclastic rocks and is divided into the Daibōgawa Rhyolite Tuff, Kumanodake Rhyolite Tuff, Kunihoro Andesite, and Funakoshi Rhyolite Tuff members. The volcanic rocks are in contact with the Kanmon Group along normal faults and with dikes intruded along the caldera faults, and they are intruded by felsites, granites, and diorites. In the west, the two formations have a half-basin structure that dips towards the Hibiki-nada Sea, whereas in the east the basin is closed. The two formations form the Nagato-Hōhoku caldera, which resembles a graben caldera. The caldera is elongated in an E-W direction and curves towards the NNE in the east, and is >34 km by >14 km. The ignimbrites of the Hōhoku and Nagato formations have subduction-related chemical compositions.

Fe oxide Liesegang bands have often been observed in sedimentary and igneous rocks, and they are formed during weathering and alteration by water-rock interactions. In this study, micro-X-ray fluorescence (μ-XRF) mapping was used to study the Fe bands in an Fe oxide concretion from the Jurassic Navajo Sandstone in Utah, USA, to estimate the duration of their formation. Most of the peaks in Fe concentration are steeper on the inner side than on the outer side, which indicates a supply of ferrous ions (Fe²⁺) from outside the concretion. The precipitation of Fe oxide was controlled by pH buffering that resulted from a reaction between acidic water and alkaline pore water that formed through the dissolution of an earlier calcite concretion. The reaction rate within the Fe oxide concretion was estimated from the width of the Fe peaks and the expected diffusion coefficient for Fe through the rock matrix, and it was found to be no more than years to decades-faster than previously estimated. This demonstrates that μ-XRF mapping is a useful technique to extract quantitative information about water-rock interactions from rocks.

Two dead specimens of the precious coral Pleurocorallium elatius were obtained from the sea-bottom surface in submarine depressions at ~350 m water depth off Zanpa Cape, Okinawajima Island. Three samples were dated by ¹⁴C analysis, and yielded ages of 32,824-31,709 and 33,685-32,911 cal BP for one specimen and 20,480-20,060 cal BP for the other. These ages suggest that there was almost no deposition of sediment for an extended period in the depressions, which are interpreted as obstacle scours on the basis of their acoustic features. The obtained ages are the oldest known for dead precious corals, suggesting that favorable chemical conditions in the sea water facilitated long-term preservation of dead coral.

A conodont fauna characterized by Streptognathodus species was recovered from a limestone block (previously called Ōboradani Formation) of the Ōtani (=Ohtani or Otani) Formation belonging to the Hida Gaien belt distributed in the Kuzuryu area, Fukui Prefecture, central Japan. The fauna consists of Streptognathodus corrugatus, S. elegantulus, S. excelsus, S. gracilis, Idiognathodus sp., Gondolella bella, G. cf. elegantula and G. cf. pohli. These streptognathodids have a wide geographic distribution and indicate a middle-late Kasimovian (Late Pennsylvanian) age, which is slightly older than the Gzhelian (latest Pennsylvanian) age infferred from fusulinid fossils in previous studies. Thus, the limestone block of the Ōtani Formation probably contains the Upper Pennsylvanian carbonate succession.

This paper describes the sedimentological, petrographic, and paleontological features of core samples recovered when drilling a seismic observation well on Shinjima Island, which emerged from the submarine floor of Aira Caldera in 1780 by magma intrusion. The results provide information on post-caldera volcanic activity and environmental change in Aira Caldera. Shortly after its formation at ~30 cal ka BP, Aira Caldera was filled with freshwater, but seawater suddenly replaced the freshwater at ~14.5 cal ka BP as sea level rose after the last glacial maximum. Sakurajima Volcano, located on the southern rim of the caldera, intermittently ejected dacitic tephras into the freshwater caldera lake, and Wakamiko Volcano, located in the northeastern part of the lake, also erupted explosively, releasing sublacustrine rhyolitic density currents over the lake floor. Lahars and floods carried much larger volumes of epiclastic material into the lake. Shortly before the transition from freshwater to seawater, Sakurajima and Wakamiko Volcanoes temporarily became calm and fine particles accumulated in the lake. The explosive eruptions at Wakamiko Volcano resumed at ~13 cal ka BP, culminating in a large eruption that formed Wakamiko Caldera and a thick accumulation of Shinjima Pumice. The explosive eruptions almost ceased with the minor eruption of the Southern Shinjima Pumice immediately after the caldera-forming event. The Southern Shinjima Pumice contains pumice and ash of the Sakurajima Satsuma tephra, indicating that the largest explosive eruption from Sakurajima Volcano occurred during the period between the eruptions of the Shinjima Pumice and the Southern Shinjima Pumice. Since the caldera-forming eruption, Wakamiko Caldera has become quiescent while Sakurajima Volcano has intermittently erupted, producing fallout tephras and lava flows. The Sakurajima tephras and volcaniclastic materials reworked from surrounding areas have accumulated on the submarine floor of Aira Caldera.

The average S-wave velocity and peak frequency of the microtremor H/V spectrum, or the resonance frequency of the ground, were estimated at 16 sites in the Tokyo Lowland along the coast of inner part of Tokyo Bay, central Japan. The results indicate that the resonance frequencies become lower with an increase in thickness of the post-Last Glacial Maximum (LGM) deposits. The post-LGM deposits are divided into the lower Nanagochi Formation and the upper Yurakucho Formation in the Tokyo Lowland. The depth of the S-wave velocity discontinuity, which determines the resonance frequency of the ground, was calculated by applying the quarter-wavelength law. At 7 of the 13 microtremor observation points examined (i.e., 3 points on a buried flat surface are excluded from the examination), the S-wave velocity discontinuity is located within alternating layers of sand and mud in the Nanagochi Formation, even though the boundary between the Nanagochi and Yurakucho formations has conventionally been considered the most significant boundary in terms of physical properties in the post-LGM deposits. This discrepancy is perhaps caused by the strong influence of either the lithologic boundaries in the alternatin layers of sand and mud in the upper part of the Nanagochi Formation, or the more conspicuous boundary at the top of the basal gravels of the Nanagochi Formation, or both. The variations in the peak frequency of the H/V spectrum are caused by the heterogeneity of meandering river and estuary deposits in the Nanagochi Formation.

Geological records of tsunamis along the Tsugaru Strait in southwestern Hokkaido, Japan, were investigated. Event deposits were identified in lowland peat at four survey sites located 100-450 m from the present coastline and 2.2-6.6 m above the present sea level. The event deposits are several centimeters thick and consist of well-sorted fine- to medium-grained sand. Based on radiocarbon dating and tephrochronology, the sedimentary ages of the event deposits were determined to be 589-516, 734-670, 1656-1538, 1745-1639, 2401-2265, and 2771-2618 cal yBP. Comparison of the clastic composition and roundness of the event deposits with those of nearby beach and river sands revealed that most of the provenance of the event deposits are beach sands. Whereas, some of the event deposits were sourced from volcanic-ash sands, which were distinct from both beach and river sands. The chemical compositions of volcanic glasses and mineral grains indicate that the volcanic ash did not originate from any known Quaternary tephra in this region. Considering the source of the event deposits, as well as the inundation distance from the coastline and the infrequency of events, the event deposits were likely formed by tsunamis. Volcanic-ash sands may have been widespread in the seafloor beyond the foreshore and were transported by tsunamis. From the sedimentary ages and depositional rates of event deposits and peat, the youngest event deposits were formed in the 13-15th century, and may be correlated with a tsunami that reached the eastern coast of Hokkaido in the 13-14th century or the AD 1454 Kyotoku tsunami. Neither the well-known 17th century tsunami that was triggered along the Pacific coast of eastern Hokkaido nor the AD 1611 Keicho-sanriku tsunami appear to have left deposits in this area. These results can be used to determinate accurately the source area of 17th century tsunamis.

An exotic block of garnet-bearing schist has been found at the boundary between the Early Triassic Takinosawa Unit of the Nedamo Belt and the Early Jurassic Nakatsugawa Complex of the North Kitakami Belt, NE Japan. This is only the second discovery of exotic schists in the Nedamo Belt; the previously identified schists occur at the boundary between the Takinosawa and early Carboniferous Tsunatori units of the Nedamo Belt. The garnet-bearing schist is characterized by a mineral assemblage of garnet + phengite + epidote + albite + quartz + titanite. Phengite with Si of 6.51-6.66 atoms per formula unit (O = 22) and the mineral assemblage suggest that the schist underwent high-P/T metamorphism prior to emplacement into its current position. The schist yields a phengite K-Ar age of ca. 290 Ma (late Paleozoic), suggesting a correlation with high-P/T schist of the Yamagami Metamorphic Rocks from the Motai-Matsugadaira Belt. This finding supports the extension of late Paleozoic high-P/T metamorphic rocks (i.e., the Renge Belt of SW Japan) to NE Japan.