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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CSIRO PUBLISHING  

This article describes a method for processing microtremor records from a small-scale seismic array that allows interval-averaged S-wave velocities to be estimated for 10-m depth ranges down to a depth of 30 m. The method was applied to microtremor data obtained in the town of Mashiki, Kumamoto Prefecture, Japan, and the analysis results were evaluated through a comparison with available PS logs and sections obtained by surface-wave methods. It turned out that the interval-averaged S-wave velocity estimates may be subject to errors of up to 20-30% in absolute values, but it was shown that the method can help evaluate relative spatial variations in those S-wave velocities. In view of the simplicity of analysis, the analyser-independent nature of the results and the limitations of analysis accuracy, the interval-averaged S-wave velocity estimation method presented here could be used as an effective tool for the preliminary analysis of microtremor data from small-scale seismic arrays.

DOI： 10.1071/EG18020

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Tokyo Geographical Society  

The 2011 off the Pacific coast of the Tohoku earthquake caused severe liquefaction events in the Kanto region, which is 300-400 km south of the earthquake's epicenter. All-core drillings and trenching surveys were carried out at Yodaura and Mukoya, which are situated in the lowland along the lower Tone River in the central Kanto region. The Yodaura site is on reclaimed land where a former lake was filled in by sand pumping from 1969 to 1974. The sediments at Yodaura consisted of silts and clays of the former Lake Yodaura deposits (natural sediments) and sandy strata composed of artificial fill. No evidence was found of liquefaction in the natural deposits, but the artificial-fill deposits suffered severe liquefaction. Three distinct sand dikes (yS1 sand dyke–yS3 sand dyke) cut the artificial strata at Yodaura: yS1 sand dyke, composed of gray, unoxidized sand, reached the ground surface and cut yS2 sand dyke, which was composed of light-brown, oxidized sand. Therefore, two liquefaction events occurred at the same point: the older event, which produced yS2 sand dyke, was probably induced by the 1987 off the east coast of Chiba Prefecture earthquake (<i>M</i>j = 6.7), and the newer one, which produced yS1 sand dyke, was induced by the 2011 earthquake. The third sand dike (yS3 sand dyke) originated in a bed of fine to medium sand containing shell fragments in the artificial strata and contained fragments of asphalt from the ground surface. This dike is consistent with eyewitness accounts of sand gushing during the 2011 event. These accounts report that the ground pulsated at intervals of several seconds, and water and sand spouted from the ground simultaneously with each ground motion pulse. The presence at Yodaura of massive un-stratified sand beds within well-stratified sandy layers, especially near the sand dikes, indicates that liquefaction destroyed the original structure of the sediments. The Mukoya site is on reclaimed land where an abandoned channel of the Tone River was artificially filled in after 1956 by sand pumping and sediment dredging. The surface sediments at the Mukoya site are composed of Holocene floodplain deposits, abandoned channel sediments deposited between 1626 and 1956, and artificial strata. Two distinct deformation structures (mS1 and mS2) were observed in a trench wall. mS1 was a sand dyke that originated in the upper member of the abandoned channel sediments and reached the ground surface. The mS1 sand dyke consisted of liquefied materials derived from the dredged fine to medium sand deposits of the lower part of the artificial strata, and where it was ejected, a “shoulder-like” point formed on the upper surface of the sandy dredged deposits. Structure mS2 was a depression structure in the lower part of the artificial strata that displaced the sandy dredged deposits and an underlying buried soil layer downward. A “sill-like” horizontal sand dike extended from the sandy deposits into the buried soil. In the muddy upper part of the artificial strata, there were many fractures parallel to sand dyke mS1 and the “shoulder” of the sandy dredged deposits. The presence of these fractures indicates that minor subsurface geological structures affected the ground motion and location of liquefied sites caused by the earthquake.

DOI： 10.5026/jgeography.127.361

DOI： 10.5026/jgeography.127.357_references_DOI_Ss96ekqlII9MC5v2IFIbZ6YfGVP

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Other Link： http://id.ndl.go.jp/bib/029135451

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本地質学会  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：TOKYO GEOGRAPHICAL SOC  

The 2011 off the Pacific coast of the Tohoku earthquake caused severe liquefaction events in the Kanto region, which is 300-400 km south of the earthquake's epicenter. All-core drillings and trenching surveys were carried out at Yodaura and Mukoya, which are situated in the lowland along the lower Tone River in the central Kanto region. The Yodaura site is on reclaimed land where a former lake was filled in by sand pumping from 1969 to 1974. The sediments at Yodaura consisted of silts and clays of the former Lake Yodaura deposits (natural sediments) and sandy strata composed of artificial fill. No evidence was found of liquefaction in the natural deposits, but the artificial-fill deposits suffered severe liquefaction. Three distinct sand dikes (yS1 sand dyke-yS3 sand dyke) cut the artificial strata at Yodaura: yS1 sand dyke, composed of gray, unoxidized sand, reached the ground surface and cut yS2 sand dyke, which was composed of light-brown, oxidized sand. Therefore, two liquefaction events occurred at the same point: the older event, which produced yS2 sand dyke, was probably induced by the 1987 off the east coast of Chiba Prefecture earthquake (Mj = 6.7), and the newer one, which produced yS1 sand dyke, was induced by the 2011 earthquake. The third sand dike (yS3 sand dyke) originated in a bed of fine to medium sand containing shell fragments in the artificial strata and contained fragments of asphalt from the ground surface. This dike is consistent with eyewitness accounts of sand gushing during the 2011 event. These accounts report that the ground pulsated at intervals of several seconds, and water and sand spouted from the ground simultaneously with each ground motion pulse. The presence at Yodaura of massive un-stratified sand beds within well-stratified sandy layers, especially near the sand dikes, indicates that liquefaction destroyed the original structure of the sediments. The Mukoya site is on reclaimed land where an abandoned channel of the Tone River was artificially filled in after 1956 by sand pumping and sediment dredging. The surface sediments at the Mukoya site are composed of Holocene floodplain deposits, abandoned channel sediments deposited between 1626 and 1956, and artificial strata. Two distinct deformation structures ( mS1 and mS2) were observed in a trench wall. mS1 was a sand dyke that originated in the upper member of the abandoned channel sediments and reached the ground surface. The mS1 sand dyke consisted of liquefied materials derived from the dredged fine to medium sand deposits of the lower part of the artificial strata, and where it was ejected, a "shoulder-like" point formed on the upper surface of the sandy dredged deposits. Structure mS2 was a depression structure in the lower part of the artificial strata that displaced the sandy dredged deposits and an underlying buried soil layer downward. A "sill-like" horizontal sand dike extended from the sandy deposits into the buried soil. In the muddy upper part of the artificial strata, there were many fractures parallel to sand dyke mS1 and the "shoulder" of the sandy dredged deposits. The presence of these fractures indicates that minor subsurface geological structures affected the ground motion and location of liquefied sites caused by the earthquake.

DOI： 10.5026/jgeography.127.361

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Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.14863/geosocabst.2018.0_85

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DOI： 10.14863/geosocabst.2018.0_84

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DOI： 10.14863/geosocabst.2018.0_81

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DOI： 10.14863/geosocabst.2018.0_83

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Although extensive research on tsunami deposits has been conducted on the Pacific coast of Japan, such deposits on the Sea of Japan coast have received little attention. Consequently, little is known about tsunamis along this coastline, especially for events that occurred before the 19th century. The aim of the present study is to enhance this record based on tsunami deposits in Lake Kamo and Iwafune Lagoon in the Niigata area.
Based on analysis of six borehole cores, twenty-four likely tsunami deposits that formed during the last approximately 9000 years were identified in Lake Kamo, and nine likely tsunami deposits that from between approximately 9000 and 2200 cal BP were identified in Iwafune Lagoon.
The likely tsunami deposits of Lake Kamo and Iwafune Lagoon have revealed the first detailed tsunami history for the last approximately 9000 years in the northern Sea of Japan. (C) 2017 Elsevier Ltd and INQUA. All rights reserved.

DOI： 10.1016/j.quaint.2017.05.045

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DOI： 10.23917/forgeo.v31i1.3977

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

<p>The 2015 Kanto-Tohoku Torrential Rain that hit the Kanto and Tohoku regions of eastern Japan from September 9 to September 12, 2015, resulted in a major riverine and slope disaster. Overbanking and breaching occurred along the central part of the Kinu River and formed crevasse splays on the flood plain around Kami-Misaka, Joso City, Ibaraki Prefecture. We clarified the distribution of crevasse splay deposits based on an interpretation of aerial photographs taken just after the disaster and a field survey. In addition, we performed an excavation survey and grain size analysis of the crevasse splay deposit. These resulted in the following findings.</p><p>1) Crevasse splay deposits mainly comprise fine to medium sand and can be divided into the following three units : Unit A, sandy silt to fine sand layer showing upward coarsening ; Unit B, fine to medium sand layer showing upward fining ; and Unit C, fine to medium sand layer with parallel lamination and low-angle cross-stratification.</p><p>2) The difference between these units probably corresponded to the changes in flow conditions during the flooding. Unit A, deposited at the early period of flooding, was derived from heavy rain and overbank of the river water ; Unit B, deposited during hydraulic bore, was generated by the breach of the river bank, flowing down the flood plain ; Unit C was formed by the flooding flow from the Kinu River via the breach point during the flood.</p><p>3) Typical stratigraphy of crevasse splay deposits in this study is characterized by the upward-fining unit (Unit B), which shows a difference from the known flood deposits.</p>

DOI： 10.4116/jaqua.56.37

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DOI： 10.5026/jgeography.126.731

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

<p>Extensive research has been conducted on tsunamigenic deposits along the eastern margin of the Japan Sea since the 2011 Tohoku Earthquake and tsunami. This paper reviews the characteristics of the large known tsunamis and the possible tsunamigenic deposits identified in this region. We have also reconstructed the spatio-temporal distribution, and a provisional correlation, of the tsunamigenic deposits in order to estimate the tsunami recurrence intervals and their wave source regions.</p><p>Most of the tsunamigenic deposits were recognized in peaty and marshy deposits found on swales of coastal dunes, flood plains, and small valley plains. Large numbers of tsunamigenic sandy layers were also identified in lagoonal deposits. In addition, some gravelly deposits of possible tsunamigenic were recognized on top of low-lying marine terraces and slope talus.</p><p>Although several historical tsunamis in the 18-19th centuries have been recorded along the eastern margin of the Japan Sea, there are few localities where deposits can be correlated to these records. Tsunamigenic deposits suggest that four tsunami events have occurred during the 9-14th centuries, despite there being limited historical records of tsunamis older than the 18th century. The distribution of these four deposits is as follows: 14th century = Aomori-northern Yamagata; 12th century = southwestern Hokkaido; 11th century (?1092 AD) = Sado/Niigata-southern Yamagata; 9th century (?850 AD) = (Sado)-Yamagata-Aomori. These events are also recorded in the deep-sea Japan Basin as seismo-turbidites. Most tsunamigenic deposits older than the 9th century have only been identified at remote islands (Okushiri, Tobishima, and Sado).</p><p>Several unanswered research questions on these tsunamigenic deposits remain, such as robust identification of the origins and precise ages of the deposits. Our work provides a framework for future screening of potential tsunamigenic deposit data and an improved understanding of paleotsunami events along the eastern margin of the Japan Sea.</p>

DOI： 10.5575/geosoc.2017.0054

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Primary tephra layers can provide isochrons in a stratigraphic sequence. Such isochrons are powerful tools in terms of correlation and chronology of strata, and they constrain a chronological framework for geology, geomorphology, archaeology and palaeo-environmental studies in the Neogene to Quaternary. However, reworking processes can re-distribute tephra materials in both time and space, so that a given tephra can form a new discrete layer later in the depositional sequence, or it can be distributed in low concentrations (no visible layers, i.e., crypto-tephras) over a range of different stratigraphic horizons. The present study, based on sedimentological, petrographical, and geochemical analyses of reworked tephras in Japan, evaluates the duration and persistence of reworking and the tephra mobilisation and delivery to watersheds. Furthermore, it discusses how a unique isochron can be constructed from tephra distribution in a sedimentary sequence. Examples presented here are from fluvial and deltaic sequences in the Japanese Quaternary, which contain several visible tephra layers and a certain amount of tephra materials from multiple sources at different stratigraphical horizons. In the Niigata Plain, 5.4 ka Numazawako tephra material continued to be reworked for more than 4000 years after the eruption of Numazawa volcano, and was re-deposited as reworked pumice grains consisting of a "visible" tephra layer in delta front deposits. Mixed tephra materials originating from an earlier eruption of Numazawa volcano and eruptions from other calderas were also identified. In the Tsugaru Plain, post-2.5 ka subsurface deposits have &gt; 10% glass shards content throughout the sequence. Glass shards were derived from several different tephra materials, such as those from the most recent eruption of Towada volcano (AD 915), and earlier caldera forming eruptions (30 ka, 15 ka). Some of the glass shards probably originated from erosion of exposed Pliocene pyroclastic bedrock. Thus, tephra reworking processes in alluvial to shallow marine settings can continue long after an eruption has ended, and can persist even during inter-eruptive (i.e., background sedimentation) periods. As tephra reworking involves complicated processes, careful observation and interpretations are necessary to evaluate whether tephra materials can truly provide an isochron for the strata in which they are found to exist. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.

DOI： 10.1016/j.quaint.2015.03.022

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

<p>Okushiri Island, located in southwest Hokkaido, Japan, was hit by an earthquake-generated tsunami in July 1993. An excavation survey revealed several event sand beds, interbedded with peaty sediments, in the lowland at the southernmost part of the island. These beds consist of relatively well-sorted fine- to medium-grained sand similar to sandy shoreline deposits; they are normally graded, fining and thinning landwards. Some beds show partial erosional bases and ripple cross-laminations, implying landward-directed paleocurrents, and grain fabrics also indicate the landward dispersal of clastics. The sand beds yield marine organic-walled microfossils such as dinoflagellate cysts and foraminiferal linings. These findings indicate that the sand beds are of tsunami origin. The results of carbon-14 dating and tephrochronology indicate that at least six tsunami events, including the AD 1741 Oshima-Ohshima and the AD 1993 Hokkaido Nansei-Oki tsunamis, have hit the island over the past 3000-4000 years.</p>

DOI： 10.5575/geosoc.2016.0042

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：関東第四紀研究会  

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DOI： 10.4116/jaqua.55.169

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Language：Japanese   Publisher：The Geological Society of Japan  

This presentation has been canceled on the day of the Annual Meeting. Please don't quote this Abstract.

DOI： 10.14863/geosocabst.2016.0_351

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DOI： 10.14863/geosocabst.2016.0_038

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DOI： 10.14863/geosocabst.2016.0_036

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DOI： 10.14863/geosocabst.2016.0_037

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DOI： 10.14863/geosocabst.2015.0_321

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：日本堆積学会  

DOI： 10.4096/jssj.73.3

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Geoinformatics  

DOI： 10.6010/geoinformatics.25.4_189

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：佐渡市教育委員会  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PALAEONTOLOGICAL SOC JAPAN  

Gasterosteus kamoensis sp. nov. is described from the Upper Miocene Minamiimogawa Formation in Kamo City, Niigata, Japan. The new species represents the oceanic complete morph. It is characterized by: short and high ectocoracoid; presence of posttemporal bone; fully developed pelvic girdle with convex anterior margin; wide and not tapering posterior process of pelvic bone; four dorsal spines; comparatively long spines in dorsal, pelvic and anal fins; and large body size, apparently exceeding 130 mm in standard length. Gasterosteus kamoensis sp. nov. is the third nominal fossil species of this genus described from East Asia, along with freshwater G. orientalis Sytchevskaya and the marine G. abnormis Gretchina. Together, these discoveries demonstrate the wide distribution and morphological and ecological diversity of this genus during the Miocene in the northwestern Pacific.

DOI： 10.2517/1342-8144-16.4.318

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

Twelve tephra beds (NB1 to NB12) are identified in peaty bog sediments on the summit of Mt. Naebasan, central Japan. Radiocarbon data from the sediments shows that the peaty deposits and tephra beds were deposited during the Holocene. On the basis of petrographic characteristics, refractive index, and chemistry of glass shards, the following correlation with previously reported tephras is suggested : NB3 tephra with Kikai-Akahoya tephra mixed with Myoko-Akakura tephra ; NB8 with Kusatsu-Shirane-Kumakura pumice ; NB10 with Kusatsu sp1-3 tephra ; NB11 with Myoko-Otagirigawa tephra ; and NB12 with Koyaike volcanic ash group C. Glass shard chem- istry suggests that the remaining uncorrelated tephra layers were probably derived either from Asama, Kusatsu-Shirane, Myoko, or Niigata-Yakeyama volcanoes.

DOI： 10.4116/jaqua.52.241

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A study of the 2011 Tohoku-oki tsunami deposits on the coastal lowland of the Sendai Plain, Japan was carried out along a shore-perpendicular survey line in the Arahama area. Field descriptions and tsunami water depth measurements were complemented by sedimentary analyses, including grain size, grain fabric and diatom analysis. The tsunami deposits show a generally fining-inland trend along the 3.4 km long transect. The depositional facies, grain size analysis and grain fabric data suggest that most of the tsunami deposits were laid down during the tsunami inflow, except at one site. These tsunami deposits are characterized by parallel-laminated or massive sand and silt with pieces of woods, fragments of glass, rip-up mud clasts and an erosional base. Minor backwash deposits overlying the inflow sand layer were only observed on one beach ridge and attributed to the topographic high. Marine diatom species comprised only approximately 2% of the diatom assemblage in tsunami deposits and their content decreased landward. In this study, diatom assemblages were similar in the rice field soil and tsunami layers, suggesting that the muddy fraction of the deposits mainly consists of sediments derived from the tsunami-eroded rice field soil. As a result of soil erosion, the tsunami had a high suspended sediment load. Furthermore, after the first tsunami inundation, seawater left by the tsunami did not drain completely to the sea because of the high coastal beach ridge and/or coastal subsidence due to the massive earthquake. Therefore, strong tsunami outflows to the sea did not occur and these areas were covered by mud deposited from stagnant water. (c) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.sedgeo.2012.07.004

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Other Link： http://hdl.handle.net/10191/16702

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：地盤工学会  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

The Echigo Plain, which faces the Sea of Japan in northeast Japan, is a typical coastal plain with numerous sand dunes. We examined the sedimentology of pumiceous sediments (lahar deposits) in the Agano River area of the Echigo Plain, derived mainly from a large-scale dam-break flood after the Numazawako eruption (about 5 ka), using an existing borehole dataset and facies analysis of sediment cores.<br>The lahar deposits show different sedimentary facies in coastal areas versus the shallow marine environment. Coarse-grained pumiceous sediments (5—8 m thick) are interpreted to have been deposited under the delta front or in a delta plain environment in a coastal area. Sandy silt deposits (pro-delta facies), including pyroclastic material (horizons of concentrated volcanic glass shards and heavy minerals), are distributed in the shallow sea area.<br>The large volumes of volcaniclastic sediment delivered during the flood event induced the rapid progradation of the delta system in the Agano River region. The deposition of volcaniclastic sediments in the shallow sea also caused progradation of the delta system and changed the coastal landforms along the margin of the Echigo Plain.<br>The flood event resulted in an increase in the progradation rate of the depositional system from 0.9 to 2.5 km per 1000 years. An understanding of large-scale pyroclastic resedimentation can contribute to evaluating and predicting the volume of sediment discharge and the nature of hazards created by a volcanogenic flood and its aftermath in an alluvial plain setting.

DOI： 10.5575/geosoc.117.483

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DOI： 10.14863/geosocabst.2011.0.339.0

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Other Link： http://hdl.handle.net/10191/12854

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japanese Society for Active Fault Studies  

The Kakuda-Yahiko fault is a west-dipping blind thrust along the western margin of the Niigata plain, central Japan. The slip rate has not clearly estimated because the fault is buried under thick sediments. We obtained and analyzed three core samples (GS-KNM-1, GS-SGT-1, and AK-1) crossing the fault, and we recognized the Holocene vertical movement on the basis of correlation of detailed description, radiocarbon ages, and diatom assemblages. Based on these analyses, we interpreted nine sedimentary facies: the late Pleistocene marine sediments, meandering river sediments, salt to freshwater marsh sediments, offshore sediments, lower and upper shoreface sediments, foreshore sediments, modern river sediments, dune sediments, and surface soils, in ascending order. The average vertical-slip rate is estimated 3.6-4.6 mm/yr based on the vertical-offsets of the ravinement surface dated 9.4-8.2 cal kyr BP and the pumice layer dated 6-5 cal kyr BP. However, this slip rate might contain at best 1.3 mm/yr compaction effects of unconsolidated muddy sediments. Therefore, the average vertical-slip rate of Kakuda-Yahiko fault would be estimated about 3 mm/yr.

DOI： 10.11462/afr.2010.32_9

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DOI： 10.14863/geosocabst.2010.0.83.0

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DOI： 10.14863/geosocabst.2010.0.349.0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Volcanic activities can create cataclysmic hazards to surrounding environments and human life not only during the eruption but also by hydrologic remobilisation (lahar) processes after the cessation of eruptive activity. Although there are many studies dealing with the assessment and mitigation of volcanic hazards, these are mostly concentrated on primary eruptive processes in areas proximal to active volcanoes. However, the influence of volcaniclastic resedimentation may surpass the impacts of primary eruptive activity in terms of both extent and persistence, and can ultimately result in severe hazards in downstream areas.
Examination of the volcaniclastic successions of non-marine Pliocene-Holocene sedimentary basins in Japan has revealed hydrological volcaniclastic sedimentation in fluvial and lacustrine environments hundreds of kilometres from the inferred source volcano. Impacts on these distal and often spatially separated basins included drastic changes in depositional systems caused by sudden massive in fluxes of remobilised pyroclastic material. Typical volcaniclastic beds comprise centimetre-to decimetre-thick primary pyroclastic fall deposits overlain by metre- to 10s of metres-thick resedimented volcaniclastic deposits, intercalated in sedimentary successions of non-volcanic provenance. The relatively low component of primary pyroclastic fall deposits in the volcaniclastic beds suggests that: 1) potential volcanic hazards would be underestimated on the basis of primary pyroclastic fall events alone; and 2) the majority of resedimented material was likely derived from erosion of non-welded pyroclastic flow deposits in catchment areas rather than remobilisation of local fallout deposits from surrounding hillslopes.
The nature, distribution and sequence of facies developed by distal volcaniclastic sediments reflect the influence of: 1) proximity to ignimbrite, but not directly with the distance to the eruptive centre; 2) ignimbrite nature (non-welded or welded) and volume; 3) temporal changes in sediment flux from the source area; 4) the physiography and drainage patterns of the source area and the receiving basin, and any intervening areas; and 5) the formation of ephemeral dam-lakes and intra-caldera lakes whose potential catastrophic failure can impact distal areas. Models of the styles and timing of distal volcaniclastic resedimentation are thus more complicated than those developed for proximal settings of stratovolcanoes and their volcaniclastic aprons and hence present different challenges for hazard assessment and mitigation. (C) 2009 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.sedgeo.2009.04.016

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This paper presents the results of detailed studies of the Budokubo Collapse Basin, which was formed in the Latest Pleistocene. The basin is located in the northern part of Uonuma Hills, attacked by the 2004 Mid-Niigata Earthquake. The basin is surrounded by hills, and the topography of the basin is a polygon, 2km long and 1.5km wide. The Budokubo Formation within the basin is composed of irregularly alternating beds of gravels, sands and silts, intercalated with the Aira Tn tephra bed (AT; approx. 2.6〜2.9ka). The formation contains peat layers which characterized static slack - water environments. The marginal facies of the Budokubo Formation are poorly sorted, and the formation is in high-angle unconformable contact with Neogene basement. The investigation reveals that just before the Budokubo Collapse Basin was formed, the main stream of the Shinano River had run through the area studied. Four step fluvial terraced surfaces are recognizable in the basin. The forming process of the Budokubo Collapse Basin is considered as follows: At first, we estimate the land was uplifted more than 25m, in a larger area containing the studied area that included the Shinano River, so, the stream had its way blocked and took another course. Later, the land collapsed approximately 25m in this small area called Budokubo. The process and the scale of the Budokubo Collapse Basin are almost the same as those of the Tamugiyama Collapse Basin, about 5km south of the Budokubo Collapse Basin, an area reported on in 2006. Moreover, these basins were formed during the same period. These facts suggest that the upheaval movement preceding the collapse movement occurred in a wide range of the region including the two basins. The region is inferred to contain Yamamotoyama Block and the place where the Uono River joins the Shinano River, which are near the two basins. In the Yamamotoyama Block, the land has been vigorously uplifted since the Latest Pleistocene. Along the junctions of the smaller blocks within the uplifted region both rivers obviously wind their way. These phenomena apparently resulted from active movements like upheaval in this region. The geodetic survey data by the Geographical Survey Institute indicate that the area of the Budokubo Collapse Basin corresponds to the highest uplifted segment in the 2004 Mid-Niigata earthquake. The eleven step fluvial terraced surfaces show that active and intermittent upheaval movements repeatedly followed from the Late Pleistocene to Holocene in this area. Therefore, this sequence of active movements in this region appears to follow the 2004 Mid-Niigata earthquake.

DOI： 10.15080/agcjchikyukagaku.63.3_167

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DOI： 10.1130/B26159.1

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

The Echigo Plain facing the Sea of Japan is a typical coastal plain covered by coastal sand dunes. Depositional systems along the lower Agano River have been clarified by the facies analysis of borehole datasets and by four newly obtained sediment cores. The upper parts of the alluvium in this area have been formed as a delta system with strong influence of the Agano River. This system is in contrast with a barrier-lagoon system, the subsiding area along the Shinano River in the Echigo Plain. Therefore, it is evident that the alluvium of the Echigo Plain has been formed by the progradation of two different depositional systems, a delta system under the influence of the Agano River and barrier-lagoon system under the impact of the Shinano River.

DOI： 10.4116/jaqua.47.191

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DOI： 10.14863/geosocabst.2008.0.423.0

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DOI： 10.14863/geosocabst.2008.0.116.0

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A detailed diatom analysis of one drilling core was carried out in the Fukushima-gata Lagoon area of the northern part of the Echigo Plain, which is situated in the inlet side of the Kitakanbara-gata Lagoon. 11 diatom divisions were detected and correlated with divisions of the Shiunji-gata Lagoon area (Yasui et al. 2002) situated in the inside part of the Kitakanbara-gata Lagoon. The characteristics of diatom assemblages and Holocene sedimentary environments of the Kitakanbara-gata Lagoon are discussed in this paper. Diatom assemblages of the Kitakanbara-gata Lagoon were characterized by flourish or decline of several maker planktonic species. In the Fukushima-gata Lagoon area three types of diatom assemblage appeared repeatedly. The first type is dominated by Aulacoseira granulata, which indicates limnophilous fresh surface water, and may be caused by a closure of an inlet. The first type took the place of the second type dominating by Cyclotella caspia, which is caused by an inflow of marine water from an inlet opening. The third type is characterized by a low frequency of planktonic species, which indicates rheophilous fresh surface water or a reduction of water area. The Holocene sedimentary environments of the Kitakanbara-gata Lagoon are identified as follows on the basis of diatom divisions and ^<14>C datings. The Kitakanbara-gata Lagoon was under a brackish lake environment in ca. 8,000 yrs BP, and three periods of marine surface water expansion occurred at ca. 6,500, from ca. 6,000 to ca. 5,000 and at 3,500 yrs BP. In ca. 3,000 yrs BP, the connection of the water area between Fukushima-gata Lagoon and Shiunji-gata Lagoon areas in the Kitakanbara-gata Lagoon were disappeared.

DOI： 10.15080/agcjchikyukagaku.61.1_49

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DOI： 10.15080/agcjchikyukagaku.61.3_171

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DOI： 10.3720/japt.71.337

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This paper shows that the Tamugiyama Basin was formed during the Latest Pleistocene by repeated uplift and collapse fault activities. The Tamugiyama Collapse Basin is the youngest one, has ever been reported collapse basins in the Japanese Islands. The Tamugiyama Collapse Basin is located in the northern part of Uonuma Hills, and is attacked by the 2004 Niigata Chuetsu earthquake. The lozenge-shaped basin, about one to two kilometers wide, is surrounded by hills composed of the Pliocene basement. The Tamugiya Formation within this collapse basin is in high-angle abut unconformity contact with Pliocene basement. Talus deposits are recognized on the unconformities. The deposits are resulted from fault scarp and its ancient slope failures. The Tamugiyama Formation is composed of irregularly alternating beds of gravels, sands and silts, intercalated with the Aira Tn tephra bed (AT) about 26,000〜29,000 years ago. The formation contains peat layers, which characterize static slack-water environments. The Kowakita Formation, underlying the Tamugiyama Formation, consists of fluvial gravels carried by the Uono River, therefore it suggests that there was once the ancient Uono River running through this area. The rapid change in sedimentary environments, from the Kowakita formation to the Tamugiyama Formation, results from uplift, faulting and collapse caused by tectonic block movements in this area. The Uono River had changed its course by fault activity and uplift just before the Tamugiyama Collapse Basin was formed, not by subsidence of the present Uono River course. The Yamamotoyama tectonic block including this study area has been the most active uplift block in the Shinano Valley since the Late Pleistocene. The 2004 Niigata Chuetsu earthquake occurred in areas characterized by the same geological setting.

DOI： 10.15080/agcjchikyukagaku.60.6_465

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

The Tamugiyama district in Kawaguchi Town, Niigata Prefecture is one of the most affected areas by the 2004 Mid-Niigata Prefecture earthquake. Though this district is located in a small (ca. 2 km²) basin, some colonies were damaged lightly and others severely. The worst-hit colony is located on the central part of the Tamugiyama fan underlain by thick (ca.20 m) muddy deposits with the N-values ranging from 5 to 20. On the other hand, lightly damaged colonies are located on the Tamugiyama-IV terrace underlain by gravel rich deposits with the N-values of over 50 and on the marginal area of the Tamugiyama fan. The Tamugiyama fan deposits were supplied from surrounding hill areas where weakly consolidated Pliocene to Lower Pleistocene sedimentary rocks occurred and a large number of landslides are recognized. The deposits filled a basin-like incised valley during the latest Pleistocene time. The close relationship between damages and thickness of the muddy fan deposits indicates that the fan deposits intensely amplified ground motions resulting in local severe damages. This fact is noteworthy for making seismic hazard maps.<br>

DOI： 10.5575/geosoc.112.188

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DOI： 10.14863/geosocabst.2006.0_56_2

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DOI： 10.14863/geosocabst.2006.0_153_1

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Engineering Geology  

A huge flood disaster was caused by a heavy rainfall around the Chuetsu area of Niigata Prefecture on July 13, 2004. The flood breached the levees in many places along Ikarashi-, Kariyata-, and Chigoshimizu Rivers, so that many houses were swept away and wide areas were under muddy flood water in Sanjo and Mitsuke Cities and Nakanoshima Town. In this study, we describe the damages sustained by the flood in Nakanoshima Town area and the southern area of Mitsuke City along Kariyata River, and discuss the current processes of the flood at these areas. It is clear that a surge of the flood attacked houses near by the point of levee breach at Nakanoshima Town, judging from the evidences such as the directions of scours and the traces of flood current toward the houses. The preferred orientations of inclined or fell-down houses, traffic signs, fens, etc., indicated the direction change of flood current. Though the primary surge ran powerfully toward southwest, the flood flowed westward being led to the lower topography until the direction changed toward northwest by an obstruction of natural levee. On the other hand, in the southern area of Mitsuke City, the flood current direction was restricted so much by the narrow valley plain that its flood strength increased much more. As the levee of Chigoshimizu River also breached, the older levee, which remained between the present one and fluvial terrace, was collapsed immediately. The flood current did not only lose its power when it had reached at the lowest terrace but also run up beyond the terrace and destroyed some houses standing on it.

DOI： 10.5110/jjseg.46.153

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DOI： 10.14863/geosocabst.2005.0_107_1

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DOI： 10.14863/geosocabst.2005.0_251_2

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DOI： 10.15080/agcjchikyukagaku.59.1_3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACADEMIC PRESS INC ELSEVIER SCIENCE  

Lake-level changes inferred from seismic surveying and core sampling of the floor of Lake Baikal near the Selenga River delta can be used to constrain regional climatic history and appear to be correlated to global climate changes represented by marine oxygen isotope stages (MIS). The reflection pattern and correlation to the isotope stages indicate that the topset and progradational foreset sediments of the deltas formed during periods of stable lake levels and warm climatic conditions. During warm stages, the lake level was high, and during cold stages it was low. The drop in the lake level due to cooling from MIS 5 through MIS 4 is estimated to be 33-38 m; from MIS 3 through MIS 2, it fell an additional 11-15 m. Because the lake level is chiefly controlled by evaporation and river input, we infer that more water was supplied to Lake Baikal during warm stages. (C) 2004 University of Washington. All rights reserved.

DOI： 10.1016/j.yqres.2004.06.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The Echigo Plain (=Niigata Plain) located along the Japan Sea (East Sea) is one of the largest coastal plains in the Japanese Islands. The post-Wurm glacial sediments are well developed, reaching a thickness over 140 in in the central part of the Echigo Plain. Diatom floral changes of the Holocene borehole cores from the Tsukigata and Shirone areas of the Echigo Plain in Niigata were examined to infer the paleoenvironmental changes in this part of East Asia. Over 290 diatom taxa were identified in the Tsukigata TG-1 and Shirone S9-4 borehole cores, and were divided into nine and 13 provisional diatom units, respectively. Most of the horizons analyzed were characterized by fresh water species, and their environments were inferred as marshes, bogs and small ponds. The major brackish water horizon dated as 10,000-6800yr BP in the Shirone borehole core was correlated with the Jomon Transgression, which was the Holocene maximum transgression in the Japanese Islands. Several minor sea-level changes in the Echigo Plain were also recognized for the past 6800yr, which were caused not only by global eustatic changes, but also by the relative subsidence of the basin on account of its location in a tectonically active zone. (C) 2003 Elsevier Ltd and INQUA. All rights reserved.

DOI： 10.1016/S1040-6182(03)00101-0

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The Echigo Plain in the Niigata area of central Japan is a coastal alluvial plain facing the Sea of Japan. The Plain contains several rows of coastal sand dunes. During the Holocene maximum transgression, a barrier island sand body was formed on the plain. However, the distribution of this barrier island is partially intermittent. Based on facies analysis of cores, the barrier island succession was found to be buried by alluvium in the central part of the Echigo Plain. The barrier sand bodies do occur in the central part of the Echigo Plain, but they are deeply subsided and tilted by an active fault in the western margin of the plain. The alluvium in this area records a history of subsidence and changes in the depositional system due to the movements on the active fault. (C) 2003 Elsevier Ltd and INQUA. All rights reserved.

DOI： 10.1016/S1040-6182(03)00099-5

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Language：Japanese   Publisher：The Volcanological Society of Japan  

DOI： 10.18940/vsj.2004.0_18

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DOI： 10.14863/geosocabst.2004.abst.0_185_2

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DOI： 10.14863/geosocabst.2004.abst.0_41_2

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DOI： 10.15080/agcjchikyukagaku.57.4_173

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DOI： 10.14863/geosocabst.2003.0_152_1

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DOI： 10.14863/geosocabst.2003.0_151_2

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Quaternary Research  

The upper Pleistocene and Holocene deposits in the northern Echigo Plain of central Japan are divided into lower, middle, and upper parts based on core data. The lower part was deposited from 40, 000 to 18, 000 yrs BP and consists of sand and gravel-supported conglomerate with alternating beds of sand and silt. The middle part (sedimentary unit I) was deposited from 10, 000 to 8, 000yrs BP and consists of sand and matrix-supported gravels. Facies analysis shows that the lower and middle parts comprise deposits of alluvial fan during the lowstand of sea level. The upper part (sedimentary units II and III) consists mostly of mud and sand that formed upward-coarsening sequences of lagoon-delta deposits. Detailed diatom analysis indicates that the history of the lagoon is divided into four stages. During the first stage (from 8, 000 to 5, 000yrs BP), a brackish lake environment with low salinity pervaded, due to flooding caused by a rapid rise in sea level of the Jomon transgression and the development of a sand dune. At the second stage (ca. 5, 000 yrs BP), the lagoon changed into a freshwater lake. During the third stage (from 5, 000 to 1, 000yrs BP), the lake accumulated a large amount of sandy sediments from the north to the south, and an eolian environment appeared. During the fourth stage (since 1, 000yrs BP), a freshwater area formed again, and has remained as the Shiotsugata Lagoon.

DOI： 10.4116/jaqua.41.185

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DOI： 10.4116/jaqua.41.199

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This study clarified the tephrochronology of late Pleistocene to Holocene strath terraces younger than approximately 50ka, based on their geomorphologic configuration between marker tephra and terraces, that are distributed between the Kakinoki and Suhara districts of the Aburuma River, central east margin of the Niigata Basin, central Japan. Six levels of strath terraces (Ab-I, Ab-II, Ab-III, Ab-IV, Ab-V and Ab-VI) have developed and four tephra ashes (Ab-t4, Ab-t3, Ab-t2 and Ab-t1) have fallen since approximately 50ka. Ab-t2 can be correlated with the widespread tephra As-K (Asama-Kusatsu, 13ka), Ab-t3 with AT (Aira-Tanzawa, 25ka) and Ab-t4 with DKP (Daisen Kurayoshi, 50ka). Ab-t1 is thought to have fallen after 13ka. Only the Ab-II Terrace distributed locally in the upper reaches was formed by the primary movement of the Higashinomyo landslide approximately 50ka.

DOI： 10.4116/jaqua.41.45

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Two hominid upper central incisors found in the Yuanmou Basin in southwest China in 1965 have affinities with Homo erectus fossils from Zhoukoudian, but exhibit primitive features. The Yuanmou hominid remains are alleged to be coeval with or older than African specimens dated at about 1-8 m.y.a. Recent age refinements of geomagnetic short reversal events and excursions permit assigning the Yuanmou hominid-bearing bed to the early Brunhes chron (about 0.7 m.y.a.). Magnetochronological assessments confirm that the Lantian calotte which has been dated to about 1.2 m.y.a., is the oldest reliable evidence for the emergence of Homo in eastern Asia as well as China, and that hominid fossils from Sangiran and Mojokerto, Java, do not exceed 1.1 Ma in age. These results refute the view that the genus Homo migrated into eastern Asia in the late Pliocene or the earliest Pleistocene. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1006/jhev.2002.0555

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DOI： 10.14863/geosocabst.2002.0_45_1

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DOI： 10.14863/geosocabst.2002.0_43_1

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DOI： 10.14863/geosocabst.2002.0_42_2

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DOI： 10.14863/geosocabst.2002.0_43_2

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Late Cenozoic strata bearing hominids and hominoids are distributed in the Yuanmou Basin, Yunnan, southwest China. Incisors of Homo erectus discovered in these strata in 1965 reportedly show primitive features known in Africa Hu, Acta geologica sinica 1 (1973, p. 65). However, recent paleomagnetic study has revealed that the age of the hominid correlates to the early Brunhes chron (Hyodo et al., Journal of human evolution (2001), submitted). The lithostratigraphy of the successions that yield many mammalian fossils including those of the hominid, and the record of Equus is re-examined. The successions are divided in ascending order into the Longchuan, Shagou, Gantang (newly proposed Yangliuchun and Daipojing Members) and Yuanmou (newly proposed Dainawu and Niujianbao Members) Formations, based on different lithology and sedimentary facies. The newly proposed depositional systems of the formations are in ascending order, alluvial fan, ephemeral braided river, sandy braided river, ephemeral gravelly braided river and alluvial fan systems. The change in facies and paleocurrents revealed in the successions suggest that the basin was initiated as a syncline basin at ca 3.5 Ma and was completed as an asymmetric half graben by active movement of the eastern marginal fault in the early Middle Pleistocene. © 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0277-3791(01)00023-3

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DOI： 10.14863/geosocabst.2001.0_122_2

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DOI： 10.14863/geosocabst.2001.0_188_1

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DOI： 10.4116/jaqua.39.521

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DOI： 10.15080/agcjchikyukagaku.53.4_247

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DOI： 10.15080/agcjchikyukagaku.53.6_420

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Association for the Geological Collaboration in Japan  

The middle to upper Pleistocene formations distributed around Lake Kamo, Sado Island, are divided into the Ryotsu First, Ryotsu Second. Ryotsu Third, and Ryotsu Forth Terrace Deposits, and Ryotsu Younger Fan Deposit in ascending order. The Ryotsu Third Terrace Deposit called the Katabata Formation, intercalates the Katabata volcanic ash and the drifted pumices which are correlated with Kitsugi pumice fall deposit (K3) and Sambe-Kitsugi tephra (SK), respectively. The Ryotsu Forth Terrace Deposit is called the Agata Formation, and contains the Agata volcanic ash which may be correlated with the On-Pm1 or Pm-1A tephra. Brown-colored eolian soil deposits cover the terrace deposits, and are divided into the A to D Members in ascending order. Volcanic ash layers in these members are correlated with the marker tephras as follows: Akasaka B1 ash to On-Kt, Akasaka B2 ash to Aso-4, Akasaka B3 ash to DKP, Akasaka C ash to AT, Akasaka D ash to As-K. On the basis of relationship between the terrace deposits and these marker tephras, the Katabata and Agata Formations are correlated with the Shimosueyoshi and Obaradai Formations in the Kanto Plains, respectively. Depositional sequence of upper part of the Katabata Formation shows a typical upward-coarsening succession, and was formed by progradation of fan delta system. The altitude of foreshore sediments tend to become lower northward. This suggests that they are deposited at the regressive stage. The lower sequence of the Agata Formation shows a typical upward-finning succession. The upper sequence of the Agata Formation shows upward-coarsening succession in the northern part, while the sequence in the southern part includes nearshore and coastal plain facies, lacking foreshore facies. Depositional facies change of the Agata Formation shows a transgressive-regressive cycle. The formation was in barrier-island and estuary or lagoon systems in the transgressive stage, and in coastal plain systems in the following regressive stage.

DOI： 10.15080/agcjchikyukagaku.53.5_340

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DOI： 10.14863/geosocabst.1999.0_112_1

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DOI： 10.14863/geosocabst.1998.0_P038

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A forearc basin fill of the Pleistocene Toyofusa Group in the southern part of the Boso peninsula, Japan is represented by slope to shelf sediments. The Toyofusa Group is subdivided into the Kanamaribata Formation, Ohi Formation, Higashinagata Formation, Takigawa Conglomerate, Sagashi Formation and Ikenouchi Formation in ascending order, and correlated with the middle and upper parts of the Kazusa Group. The slope to shelf sediments form a northeasterly onlapping clastic wedge and include many numbers of volcanic ash layers. Mapping of depositional associations with tracing volcanic ash time marker, together with the interpretation of depositional facies, permits identification of stratal terminations and of temporal-spatial variations of depositional environments. These enabled a precise sequence-stratigraphic analysis of the sediments of the Toyofusa Group. Seven depositional sequences have been identified in the Toyofusa Group. Each the depositional sequences show lateral terminations of depositional facies and vertical facies discontinuities at the sequence boundaries. These depositional sequences consist of complete or incomplete assemblages of fundamental components of lowstand, transgressive, and highstand systems tracts. Fission track and paleo-magnetic ages for the Toyofusa Group showed that the depositional sequences can be correlated with oxygen isotope stages of 15 to 23. By the correlations, periodic formation of depositional sequences can be attributed to glacio-eustatic sea-level changes of about 40,000 to 100,000 years.

DOI： 10.15080/agcjchikyukagaku.51.2_83

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The severest damage caused by 1995 Hyogoken-Nanbu Earthquake occurred within a narrow zone in the coastal plain between the Rokko mountains and Osaka Bay, from Kobe City to Nishinomiya City. The distribution map of the damage rate of houses indicates that the boundaries in which the damage rates change sharply lie on a straight line or segment.<br>Seismic and gravity measurements were conducted to reveal the subsurface geological structure of this coastal plain. Seismic reflection surveys were carried out along two survey lines across the zone. The gravity measurements were made at 1, 824 points, most of which have a short interval of about 25m along observation lines. The following conclusions were derived from this study.<br>(1) The seismic profiles show concealed faults below the shallow subsurface deposits in the coastal plain.<br>(2) Remarkably steep gradients of Bouguer anomalies are distributed along the boundary of the Rokko mountains and the plain.<br>(3) Estimation of the gravity structure shows that the basement dips steeply toward Osaka Bay, and that the largest step with concealed faults exists in the coastal plain.<br>The distribution of the damage rate of houses is consistent with the location of the concealed faults. In particular, the northern boundary of the severely damaged zone is situated nearly on the largest step of the basement structure. Therefore, it is concluded that the subsurface geology with concealed faults caused the seismic disaster in the coastal plain.

DOI： 10.4116/jaqua.35.165

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DOI： 10.14863/geosocabst.1995.0_185_1

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DOI： 10.15080/agcjchikyukagaku.48.1_51

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DOI： 10.14863/geosocabst.1994.0_148_2

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Language：Japanese   Publisher：新潟大学災害・復興科学研究所  

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Language：Japanese   Publisher：新潟大学災害・復興科学研究所  

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Language：Japanese   Publisher：新潟大学災害・復興科学研究所  

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Language：Japanese   Publisher：実業公報社  

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Language：Japanese   Publisher：The Geological Society of Japan  

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Language：Japanese   Publisher：The Geological Society of Japan  

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Language：Japanese   Publisher：新潟応用地質研究会  

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Language：Japanese   Publisher：新潟大学災害復興科学センター  

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Language：Japanese   Publisher：海洋出版  

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Language：Japanese   Publisher：新潟応用地質研究会  

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Language：Japanese   Publisher：東北大学大学院工学研究科東北地区自然災害資料センター  

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Language：Japanese   Publisher：Niigata University  

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J-GLOBAL

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：TAYLOR & FRANCIS INC  

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The Plio-Pleistocene Uonuma Group, well exposed in the Higashikubiki Hills of Niigata Prefecture, central Japan, attains more than 3,000 m in the total thickness. Clastic sediments of the Uonuma Group mainly consist of cyclic changes in marine and non-marine beds intercalated with many volcanic ash markers. They are divided into the Tsukayama and Oguni formations based on lithofacies features of the sediments. The marine beds interbedded with the non-marine beds suggest that the transgressive and regressive processes were controlled by glacio-eustatic sea-level changes. According to analysis of sedimentary facies, marine beds consist of inner-shelf, shore face, beach and bay-lagoon sediments. Depositional cycles of marine beds differed in the Tsukayama and Oguni formations. That is, marine beds of the Tsukayama Formation were formed by the the "Beach-Shoreface type". In contrast, those of the Oguni Formation were formed by the "Bay-Nearshore type". By correlating each marine bed with the stable oxygen isotope sea level index, based on an age framework for the Uonuma Group, integrated with the volcanic ash age and nanno-fossil analysis, the periodicity of cyclic changes in marine and non-marine sediments of the Uonuma Group can be estimated at about 40,000 to 100,000 years.

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Other Link： http://dl.ndl.go.jp/info:ndljp/pid/10810124

Language：Japanese   Publisher：Shimane University  

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Other Link： http://ir.lib.shimane-u.ac.jp/6330