HQR23-01

Room:101A

Time:May 24 10:00-10:15

Correlation of the Alluvial bed based on drilling core in the northern Chiba Prefecture
along Tokyo bay
MIYACHI, Yoshinori1∗ ; KOMATSUBARA, Junko1
1

AIST
Correlation of the Alluvial bed based on drilling core in the northern Chiba Prefecture along Tokyo bay

Keywords: Northern Chiba, Alluvial bed, drilling core, incised valley

1/1

HQR23-02

Room:101A

Time:May 24 10:15-10:30

Distribution of postglacial incised-valley fills beneath Kujukuri Plain, central Japan
KOMATSUBARA, Junko1∗
1

AIST

Kujukuri Plain, Chiba Prefecture, eastern Japan, is formed as beach ridges prograding during and after Holocene highstand(Moriwaki, 1979). Subsurface strata which is 20m thick from the ground level is composed of beach sand, and topographic relief
including incised valleys buried under the sands. The buried topographic relief of offshore in this area has been revealed to someextent by sonic prospecting (Maritime Safety Agency of Japan 2000), whereas those in the land area is almost unknown, except
for the southernmost part of the plain (Mobara Area). The topography of buried valley is estimated based on boring log data,
which is from Information Bank of Chiba Prefecture (open data) and from local governments (open/closed data). Several axesof incised valleys are located roughly along present rivers. The northernmost one is most wide and deep, which is about 40 m
deep at the coastline, and seem to connect with the largest valley offshore. We have the plan of stratigraphic boring surveys inthis area for estimation of tectonic movement and geographic development in late Quaternary.
Keywords: Kujukuri Plain, Chusekiso, postglacial incised-valley fill, Holocene

1/1

HQR23-03

Room:101A

Time:May 24 10:30-10:45

3D analysis of a sandy point bar in the Yahagi River, central Japan, using GPR survey
OKAZAKI, Hiroko1∗ ; KWAK, Youngjoo2 ; TAMURA, Toru3
1

Natural History Museum & Institute, Chiba, 2 International Centre for Water Hazard and Risk Management under UNESCO,
Public, 3 Geological Survey of Japan, AISTWe conducted a ground-penetrating radar (GPR) survey of a sandy point bar in the Yahagi River, central Japan, to clarify thethree-dimensional (3D) depositional facies. The survey was conducted in January 2015 using a 250-MHz antenna. Surveyed bar,which is 725 m long, 160 m wide, is composed of two or more rows of bars. Three-dimensional dunes characterize the surfaceof middle- lower downstream parts. We identified inclined reflections, horizontal reflections, and trough-shaped reflections in
the bar. Inclined reflections are predominant in longitudinal sections, and horizontal reflections and trough-shaped reflections arecommon in transverse sections. These reflections represent downstream migration of the bar, developments of three-dimensionaldune, chute channel during floods.
Keywords: GPR survey, sandy point bar, Yahagi River, Japan

1/1

HQR23-04

Room:101A

Time:May 24 11:00-11:15

Holocene subsidence estimated by depositional process of the Rikuzentakata plain,northeast
Japan
NIWA, Yuichi1∗ ; TODA, Shinji1 ; SUGAI, Toshihiko2
1

International Research Institute of Disaster Science, Tohoku University, 2 Graduate School of Frontier Sciences, The Universityof TokyoTime-dependent inconsistency of crustal movement is suggested in the Sanriku coast, northeast Japan. Coseismic subsidence
up to 1.3 m of the 2011 M=9.0 Tohoku-oki earthquake and a century-long subsidence rate of 1 ? 10 mm/yr is reported in theprevious study. In the north part of the Sanriku coast, this short-term subsidence apparently contradict to long-term uplift rate of
0.3-0.5 mm/yr estimated from a flight of Pleistocene marine terraces. In the south Sanriku coast, long-term crustal movement is
unknown because of fragmentary distribution of marine terrace and lack of age data.
This study detected predominance of subsidence during the Holocene from total five core data of the Rikuzen-takata plain, thesouthern Sanriku coast. On the basis of feature of core sediment, sedimentary facies was divided into braided river, tidal influenced environment, delta, and terrestrial marsh, from lower to upper, in ascending order. Age-depth curve was described basedon twenty-five 14C ages. For the estimation of Holocene vertical movement, observed relative sea-level (RSL) was comparedwith theoretical RSL. RSL at 10 to 9.0 ka was estimated at the altitude of -30 to -27 m by using altitude of depositional surfaceof tidal deposits shown by both age-depth curve and molluscan shells in intertidal zone. Estimated RSL is lower than theoretical
RSL without tectonic effect. Probable cause of this discrepancy is Holocene tectonic subsidence of the studied area.
Geologic cross-section with one thousand year isochrones on the basis of about fifty radiocarbon ages shows that sediment
stacking pattern is retrogrational at 10 to 8 ka whereas aggradational after 8 ka. Depositional landform at 6 ka, when relative
sea-level without tectonic effect is same or slightly higher than present sea-level, shown as isochrone at 6 ka is buried under thepresent delta system. This indicates predominance of subsidence during the past 6 ka. Detected subsidence is consistent withcoseisimic subsidence of the 2011 event and a century-long submergence.

Keywords: Holocene, Sanriku coast, subsidence, Rikuzentakata plain

1/1

HQR23-05

Room:101A

Time:May 24 11:15-11:30

Liquefaction-fluidization mechanism in man-made strata along Tone River at the 2011 off
the Pacific coast of Tohoku Eq.
KAZAOKA, Osamu1∗ ; KOMATUBARA, Taku2 ; MIZUNO, Kiyohide2 ; FURUNO, Kunio1 ; YOSHIDA, Takeshi1 ;MIYACHI, Yoshinori2 ; MORISAKI, Masaaki1 ; KAGAWA, Atsushi1 ; HOSOYA, Takushi3
1

Research Institute of Environmental Geology, Chiba, 2 AIST, Geological Survey of Japan. Institute of Geology and Geoinformation, 3 Chuo Kaihatsu Corporation
Many sand volcano distributed on reclaimed land by hydraulic fill around Yodaura Marsh along Tone river on the 2011 off
the Pacific coast of Tohoku Earthquake. One of the sand volcano was excavated after falling off groundwater level by well point
method. The large relief peels were took from the large trench section. Detailed stratigraphy of man-made strata was cleared andmechanism of liquefaction-fluidization was evidented.
Keywords: Liquefaction-fluidization, man-made strata, Tone River, The 2011 off the Pacific coast of Tohoku Earthquake, trench
survey1/1

HQR23-06

Room:101A

Time:May 24 11:30-11:45

A hypothesis regarding their generation and storage process about tsunami traces due to
7.3 ka Kikai caldera eruption
NANAYAMA, Futoshi1∗ ; NAKAGAWA, Shojiro2 ; SASAKI, Hiroyuki2 ; OMOTE, Masamichi2 ;WATANABE, Kazuaki1 ; NARUO, Hideto3
1

Geological Survey of Japan, AIST, 2 Yakushima Earth-science Club, 3 Takeokadai High school

Many researchers have noted that Yakushima may have been struck by a huge tsunami before the Koya pyroclastic flowat the time of the Kikai Caldera eruption about 7.3 ka, but there is currently no clear evidence of this. We studied traces of
the tsunami in the northeastern part of Yakushima, in southwestern Japan. Holocene marine terraces were observed after the
Jomon transgression near the Miyanoura lowland. From local observations, we assumed that the highest sea level phase (9.7 m)
occurred between 7.3 and 5 ka. We re-examined a previously studied outcrop near the Onagawa river mouth at the Koseda coast,and interpreted it as follows. A wave cut bench (WB-4) emerged before 7.3 ka. There is a 30-cm thick pyroclastic flow depositthat was unaffected by wave action; the lowest elevation of the bottom of the pyroclastic flow deposit is 8.4 m. We therefore
inferred that the sea level height 7.3 ka was 8.4 m or less, and that a transgression of 1˜2-m continued after 7.3 ka. In addition, apoorly sorted, 30-cm thick gravel bed was observed between the surface of WB-4 and the pyroclastic flow deposit. This gravel
bed has a very similar composition to modern gravels distributed around the Onagawa river mouth. The pyroclastic flow deposit
is covered by a fluvial reworked deposit and a 2-m thick gravel bed. The maximum annual tidal range is about 1.5 m in thisregion; the elevation of the upper surface of the gravel bed is 11.0 m. From this, we infer that the gravel bed was deposited during
the highest sea level phase. Therefore, we conclude that the 7.3 ka tsunami moved gravel from the Onagawa river mouth to thesurface of WB-4 in a stony debris flow before the pyroclastic flow reached the Koseda coast.
Keywords: Tsunami traces, 7.3 ka Kikai Caldera eruption, Koya pyroclastic flow, Koseda coast, Yakushima Island, storage
process

1/1

HQR23-07

Room:101A

Time:May 24 11:45-12:00

Radiocarbon and dendro-dates of buried woods excavated from lowland archeologicalsites in Japan
NAKAMURA, Toshio1∗ ; KIMURA, Katsuhiko2 ; NISHIMOTO, Hiroshi3 ; HAKOZAKI, Masataka1
1

Center for Chronological Research, Nagoya University, 2 Faculty of Symbiotic Systems Science, Fukushima University, 3 Facultyof Law, Aichi University
There are many wetland archeological sites in Japan, because the land consisted of small islands with rather high precipitation. Such sites preserve wooden remains, and woods are one of the very important remains that provide the ages of the sites.
In excavation of wetland sites has revealed a huge number of wooden substances used by ancient people as materials for theconstruction of residential houses, fences as well as wooden tools. To determine chronology of the sites, wood materials arenormally analyzed by radiocarbon dating of the outermost part of tree rings, or in some cases a wiggle-matching analysis isapplied. Another age estimation is tried by dendrochronology if disk samples can be collected from them. Even if precise age
estimation of the woods is not possible by dendrochronology, cross-dating analysis of wood samples would be useful. In fact,
more than 80 wooden poles excavated at the Aota site, Niigata Prefecture, were grouped temporally into two parts, and tree-ringage relations were established between the two groups by comparing the ring-width data for almost all wood poles collected.
The age difference of the two groups was estimated to be 91 years by cross-dating the ring-width patterns of the two groups byconnecting them to a ring-width pattern of one natural tree that seemed to cover the full age range extended by the two groups.
Recently, by applying 18O/16O patterns of the cellulose fraction from annual rings, instead of ring width, the accurate age of thetwo groups was successfully determined.
These analyses suggested that radiocarbon dating, dendrochronology based on ring-width patters as well as 18O/16O patternsof annual rings should be connected one another, to get a precise chronology of the woods excavated from the archeological sites.

Keywords: radiocarbon age, dendrochronology, calendar date, cross-dating, 18O/16O chronology, 14C wiggle matching

1/1

HQR23-08

Room:101A

Time:May 24 12:00-12:15

Eutrophication trends of Japanese mountain lakes inferred from sedimentary diatom assemblages
HIRATA, Keito1∗ ; KUWAE, Michinobu2 ; TSUGEKI, Narumi K.3 ; URABE, Jotaro4 ; MAKINO, Wataru4
1
3

Graduate School of Science and Engineering, Ehime University, 2 Center for Marine Environmental Studies, Ehime University,
Faculty of Law, Matsuyama University, 4 Graduate School of Life Science, Tohoku University

In recent years, atmospheric pollution caused by fossil fuel burning is growing due to economic development in East Asian
countries. Japan, which is located downwind, concerns about the transboundary atmospheric pollution which causes humanhealth damage and environmental and ecosystem deteriorations. However, studies on effect on mountain lake ecosystems arevery rare in Japan. We have studied temporal changes in Japanese mountain lake ecosystems based on paleolimnological approach to elucidate long-term effects on the transboundary atmospheric pollutant depositions on mountain lake ecosystems. Recent analyses in mountain lake sediments from Tohoku, Hokkaido, and Hokuriku indicated that phytoplankton and zooplankton
communities have changed in 1980s together with increasing coal burning in china and enhanced accumulation of coal-derived
heavy metals in the studied lakes (Kuwae et al., 2013; Tsugeki et al., 2012). However, it is still unclear what hydrological factors
associated with enhanced atmospheric pollutant depositions to the lakes have induced the changes in the plankton communities.
In this study, we examined diatom assemblages in core sediments collected from mountain lakes of Niseko-Ohnuma and Lake
Rausu in Hokkaido, Mikuriga-Ike in Toyama prefecture to elucidate changes in nutrient level and pH in the lake waters associatedwith enhanced atmospheric pollutant depositions. In Niseko-Ohnuma diatom analysis showed changes in assemblages from acidophilous and oligotrophic taxa to neutrophil and mesotrophic taxa in 1980s. In Mikuriga-ike, the result shows that oligotrophic
taxa decreased and mesotrophic taxa increased after the 1990. Meanwhile, in Lake Rausu, diatom assemblages showed minorchanges around 1980s.
These observations indicated that the increases in phytoplankton and zooplankton in mountain lake ecosystems reported previously resulted from increased levels of nutrients in lake waters. Our results supported the hypothesis that enhanced atmosphericnutrient depositions after 1980s may result in eutrophication in the mountain lakes and impact the lake ecosystems.

Keywords: eutrophication, Japanese mountain lakes, diatom assemblages, recent past

1/1

HQR23-09

Room:101A

Time:May 24 12:15-12:30

Longitudinal river profiles crossing marine terraces at northern part of western Osado
coast, Sado Island, central Japan
OGAMI, Takashi1∗
1

Chuo University

Marine-terrace development of the Middle to Late Pleistocene and Holocene at coast of Osado, northern part of Sado Island,
central Japan, indicating tectonic uplift has been described (Ota, 1964; Tamura, 1979). At northern area of the western Osado
coast, series of Pleistocene marine terraces are identified (MIS 13, 11, 9 and 5e) and Holocene marine terrace is also recognized.
Here, based on drainage analysis using high-resolution DEM, river knickpoints are identified on detailed longitudinal riverprofiles crossing the marine terraces. At 9 out of 10 rivers, major river knickpoints develop within 500 m upstream of rivermouths, those likely formed together with sea cliffs eroded during post-glacial sea-level rise and following high stands.
Retreat of sea cliffs and river knickpoints associated with coastal erosion would have finished when the Holocene marine
terraces emerged. After the emergent, the river knickpoints retreated by fluvial incision. Distances between sea cliffs and riverknickpoints could be distance of knickpoint retreat. The distances are detected as 100-150 m based on 1:25,000 topographic
maps and DEM analysis. Assuming that the emergent occured during 7-8 ka, the rates of knickpoint retreat range 12-21 m/ky.
These rates could be high enough to dissolve old river knickpoints, formed on or before the Last Interglacial period (MIS 5e).

Keywords: river knickpoint, uplift, rocky coast, coastal erosion, digital elevation model, Pleistocene

1/1

HQR23-P01

Room:Convention Hall

Time:May 24 18:15-19:30

The reports of seismic reflection survey in the eastern coastal area of Boso Peninsula
FURUYAMA, Seishiro1∗ ; SATO, Tomoyuki1
1

National Institute of Advanced Industriak Science and Tecnology

AIST has conducted the coastal project since 2008 in order to equip seamless geoinformations of land and sea (e.g., Sato,2014). This project has approached the eastern coastal area in Boso Peninsula since 2014 and this study reports the preliminary
results of the subsurface structure in the area.
Some characteristic geological structures distribute in Boso peninsula. The Kamogawa-teichi fault zone extends to east-west
direction at southern part of the Boso Peninsula (Murai and Kaneko, 1975; 1976). The Kashima-Boso uplift zone including
some uplift axes locates from the Kashima area to the Boso Peninsula (Kaizuka, 1987). Additionally the Japan trench, where thePacific plate are subducted under the Eurasian plate, is located on the east of Boso Peninsula.
The survey area is the eastern coastal area of Boso Peninsula and the total length of the survey line is 630 km. The method of
this survey is seismic reflection by boomer equipped with boats. A Streamer cable has 24 channels with 3.125 m spacing.
The survey area is subdivided into the Kujukuri area and the Kamogawa area based on topography and geological structures.
The Kujukuri area is characterized by broad shelf with 150 m in depth and existence of the Katakai canyon. Two strata boundedby unconformity distribute in this area and this study defines them as the Kujukuri A Unit and the Kujukuri B Unit, in ascendingorder. The Kujukuri B Unit has some synclines and anticlines, which strikes are toward both north-south and east-west direction.
The Kamogawa area is characterized by the Kamogawa canyon and narrow slope. The strata in the area are subdivided into
the Kamogawa A Unit and the Kamogawa B Unit in ascending order. The Kamogawa A Unit is further subdivided into somesubunits related to sea level cycle. Although there are no data for sedimentary age, the Kamogawa A Unit could correlate to the
Kujukuri A Unit. The progradation pattern forward the land can be observed within the Kamogawa B Unit. Additionally there
are some faults fallen toward westward.
The strata distributed in Kujukuri area could be correlated to the Shimousa Group and those in Kamogawa area could becorrelated to the Awa Group respectively, although more investigation should be required.

Keywords: he eastern coastal area of Boso Peninsula, seismic reflection survey, the Kujukuri area, the Kamogawa area

1/1

HQR23-P02

Room:Convention Hall

Time:May 24 18:15-19:30

Alluvium stratigraphy and basal topography in the southern part of the Kujukurihama
Lowland, central Japan
NAKASHIMA, Rei1∗ ; NANAYAMA, Futoshi1 ; OOI, Shinzou2
1

Geological Survey of Japan, AIST, 2 Geospatial Information Authority of Japan

Alluvium stratigraphy and basal topography in the southern area of the Kujukurihama Lowland, Boso Peninsula, central Japanare reconstructed on the basis of numerous number of borehole logs and radiocarbon datings. The Alluvium in this area isdivided into two patterns of succession. Pattern I is composed of estuary muds (20-30m in thickness), shoreface-beach sands (upto 20m), and lagoon-floodplain muds (about 5m), in ascending order. Pattern II, while, is almost the same as the Pattern I without
the estuary muds. Radiocarbon ages show that estuary muds and shoreface-beach sands were deposited during a transgression
stage 12,000-9,000 calBP and a highstand stage 7,000-5,000 calBP, respectively. The radiocarbon ages of shoreface-beach sands
shows younger toward the seaward, that means that the shoreface-beach sands prograded after a maximum highstand stage.
The boundary between the Alluvium and the Pleistocene deposits is recognized by N-value, which is based on the hardness of
sediments. The basal depth of the Pattern II shows that the boundary forms somewhat flat surface inclined to offshore direction.
On the basis of the distribution of the estuary muds of the Pattern II succession, several incised valleys, which direct from NW-W
to SE-E, are revealed. The incised valleys are formed by river-flow from surrounding hills into the Pacific during the Last Glacial
Maximum.
Keywords: Alluvium, incised valley, Last Glacial Maximum, Holocene, Kujukurihama, Mobara

1/1

HQR23-P03

Room:Convention Hall

Time:May 24 18:15-19:30

Paleoflood reconstruction using peat ash in the Ishikari Lowland, northern JapanISHII, Yuji1∗
1

Graduate Schoolo of Environmental Studies, Nagoya University

Previous studies of paleoflood reconstruction often focus on slackwater deposits, and they have discussed the relationshipbetween the frequencies of rare, large floods and regional climate changes. On the other hand, paleoflood reconstruction using
overbank deposits are scarce because it has many problems.
The relative amounts of the clastic sediments in peat mainly reflect the overbank sedimentation rate. The sedimentation rateof fine sediments is usually controlled by the flooding duration. Therefore, reconstruction of flood frequency can be made using
Loss on Ignition (LOI) of peat.
Ishikari Lowland is one of the largest meandering river systems in Japan, and large peatlands are distributed between rivers. I
collected sediment samples using hand-operated auger and measured LOI. Furthermore, I conducted seed analysis to clarify theconditions of nutrients. Radiocarbon dating was conducted on plant fragments, wood pieces and twigs.
The peat has approximately 3-5 m thick, and is underlain by bluish grey clay. Plant fragments are usually scarce in the clay.
The patterns of LOI can be classified into 3 categories and they are also characterized by its location. The LOI decreases from5400 to -3600 cal BP, relatively stabilizes between 3600 and 1500 cal BP, and increases after 1500 cal BP in pattern 1. Thispattern is found near the Ishikari River. The LOI just fluctuates between 20 and 80 % and long-term trend is not clear in pattern
2. This pattern occurs near tributaries. The LOI of pattern 3 is relatively high and stable (>70%). This pattern is found in eastern
margin of the lowland. The LOI of peat is consistent with the changes in nutrients conditions. Where peat LOI is low, plant
species that prefer high-nutrients conditions are found, and vice versa.
Peat LOI is determined by the balance between the overbank sedimentation rate and organic sedimentation rate. They may be
influenced by the flood frequency, magnitude of flood, temperature, and plant species composition. However, it is apparent thatthe changes in LOI are consistent with that of nutrients conditions. Nutrients conditions of peatland are usually defined by theflood frequency. Therefore, peat LOI can be used as the indicator of paleoflood frequency.
The overbank floods of the Ishikari river are usually triggered by the combination of Baiu/Akisame front and typhoon. Therefore, the LOI of pattern 1 can be interpreted as an indicator of the frequency of typhoon. The changes in typhoon frequency
estimated from this study are almost consistent with the result of major flood frequency inferred from the Lake Suigetsu deposits(Schlolaut et al., 2014).

Keywords: paleoflood, peat, floodplain, Holocene

1/1

HQR23-P04

Room:Convention Hall

Time:May 24 18:15-19:30

Identification and correlation of tephras in aeolian deposits covering marine terraces on
the northern Sanriku CoastMIYAZAKI, Mayumi1∗ ; ISHIMURA, Daisuke2 ; NIWA, Yuichi2 ; TODA, Shinji2
1

Dept. Earth Science, Tohoku Univ., 2 IRIDeS, Tohoku Univ.

Numerous geographical or geological researches on the northern Sanriku Coast have been conducted since 1960s. In the
Kamikita Plain, Miyauchi (1988) and Kuwabara (2009, 2010) revealed stratigraphic, lithologic and petrographic characteristics
of Toya tephra (112-115 ka: Machida and Arai, 2003) which is available as correlation of the Last Interglacial (LIG) marine
terraces. On the northern Sanriku Coast, although Yonekura (1966) correlated the marine terraces based on geomorphologicalanalysis and sedimentary facies, few studies focusing on the terrace ages on the basis of tephrochronology have been conductedsince then. Thus, this study concerns features of tephra layers (e.g., stratigraphic position, lithofacies, refractive index and morphological classification of volcanic glass shards) in the Kamikita Plain as a reference. We also identified tephra layers on thenorthern Sanriku Coast based on correlation to those reported in the Kamikita Plain to improve of accuracy for age estimation of
the LIG marine terraces.
In this study, we first mapped the LIG marine terraces by aerial photograph interpretation, and then conducted field surveys
and collected tephra samples. In tephra analysis, we observed grains in tephra sample under a polarizing microscope and clarified
their grain composition and shape of their volcanic glass shards. In addition, for some tephra samples refractive index of theirvolcanic glass shards were measured by using RIMS2000.
In Kamikita Plain, the Takadate surface (Miyauchi, 1985), one of the LIG marine terraces, is well developed. We collected
tephra samples (To-H, To-BP1, To-G, To-Kb, To-Ok2 , To-AP, Toya, ZP2) at Mitateyama reported as a type locality of tephras
covering the Takadate surface by Miyauchi (2001). To-H is composed of several fall units. Its volcanic glass shard content ishigh and its glass type is mainly pumice type. To-Ok2 is composed mainly of coarse-grained pumice. To-AP contains blue-graylithic fragments in the upper part of the layer. Toya appears as a gray-white ash layer. Its volcanic glass shard content is high andits glass type is characteristically bubble-wall type. We measured refractive indices of its volcanic glass shards at n=1.493-1.497.
These characteristics are similar to the ones in the previous reports (Machida and Arai, 2003; Kuwabara, 2010).
On the northern Sanriku Coast, the Taneichi surface, reported as a LIG marine terrace by Yonekura (1966), are developed
at 20-30 m a.s.l.. From field surveys, it is presumed that terrace deposits of the Taneichi surface are marine beds because they
consist of well-sorted sand layers and rounded gravel layers, which are similar to modern beach deposits. In addition, we identified four tephra layers (Tephra 1-4 in descending order) covering the Taneichi surface. The Tephra 1 is interbedded with theupper part of aeolian deposits and consist of a few fall units. Its glass type is mainly pumice type, and refractive index of its
volcanic glass shard is n=1.503-1.513. These characteristics are similar to To-H and thus we correlated this tephra with To-H.
The Tephra 3 is probably correlated with To-AP because it contains blue-gray lithic fragments in the upper part of the layer. The
Tephra 2 is probably correlated with To-Ok2 because of its stratigraphy and consistency with the thickness from an isopach map
in Miyauchi (1985). The Tephra 4 is correlated with Toya because its volcanic glass shard content is high, and its glass type ismainly bubble-wall type.
In this study, we found four tephra layers covering the Taneichi surface on the northern Sanriku Coast and preliminarily correlated them with To-H, To-Ok2 , To-AP and Toya. Consequently, we estimated that the Taneichi surface was a LIG marine terrace
because Toya covered immediately above marine beds. In the meeting, we will report more detailed petrographic characteristicsof the tephras and results of correlation and chronology of LIG marine terraces on the northern Sanriku Coast.

Keywords: the Sanriku Coast, marine terrace, tephra, Toya tephra

1/1

HQR23-P05

Room:Convention Hall

Time:May 24 18:15-19:30

Holocene paleoenvironment and crustal movement in Yamada plain, south of Sanriku
coast in northeast JapanTSUYOSHI, Yamaichi1∗ ; SUGAI, Toshihiko1 ; SHIMIZU, Hitoshi1 ; MATSUSHIMA, Yoshiaki2 ;MATSUZAKI, Hiroyuki3 ; NIWA, Yuichi4
1

Graduate School of Frontier Sciences, The University of Tokyo, 2 Kanagawa Prefectural Museum of Natural History, 3 The University Museum,The University of Tokyo, 4 International Research Insitute of Disaster Science,Tohoku University
Background,Objective
The Sanriku coast in northeast Japan forearc is a typical ria coast and has geologically uplifted but geodetically and seismologically subsided (e.g. Miyauchi, 2012) . In order to solve the paradox, Holocene lowland development in south Sanriku coast
area is a clue.
The purpose of this study is to clarify the Holocene environmental changes and crustal movement in the south of Sanriku coast
areas using drilling core sediments.
Study Area,Methods
This study focused on Yamada plain in Iwate Prefecture in south of Sanriku coast because the plain locates in a typical enclosed
environment without marked river systems and located inner part of Yamada bay, and because many borehole cores were drilled
and available.
We conducted landform classification, sedimentary facies analysis, grain size analysis, elementary analysis, diatom analysis,
identification of shell species, tephra analysis, and high-resolution AMS 14C dating.
Results,Discussion
Reconstruction of Holocene paleogeography in Yamada plain
The alluvium in Yamada plain is divided for five units, based on the facies, grain size, total sulfur content, and occurrence ofshell fossils. The paleogeography of the study area can be characterized by four stages associated with glacial eustasy as follows:
wetland in the early Jomon Transgression (about 10,000 cal BP-8,000 cal BP; unit1) ; enclosed bay after tidal flat in Jomon
Transgression (about 8,000 cal BP-4,200 cal BP; unit2) ; tidal flat or shallow marine in the eastern (sea) side (unit3) and coastal
lowland in the western side (unit4) in the period of regression (about 4,200 cal BP-300 cal BP; unit3, 4) ; and wetland or beachridge (about 300 cal BP-present; unit5) .
Holocene crustal movement in Yamada plain and south of Sanriku coastTo estimate the trend of Holocene crustal movement, we compared the age-depth curve obtained from the core and theoreticalsea level curve (Okuno et al., 2014) which does not take into account the local crustal movement. The age-depth curve when
Yamada plain was intertidal zone roughly shows local sea-level. Therefore, if the local crustal movement was not in the past,
the age-depth curve should overlap with the theoretical sea level during the same time. However, the former is clearly below
the latter, indicating that Holocene crustal movement in Yamada plain is more or less subsidence trend. In addition, the averagesubsidence rate of the past was 1.5-2.3 mm / yr at about 7,500-8,000 years, about 2.3 mm / yr at about 1,700 years.
This study revealed that the trend of Holocene crustal movement in Yamada plain is more or less subsidence trend. This result
is the same trend as it of the last 100 years. It is also suggested that the trend of Holocene crustal movement in whole south ofSanriku coast area is subsidence trend by comparing with previous study in Rikuzentakata plain (Niwa et al., 2014).
References
Miyauchi, T.(2012): Science journal Kagaku, 82, 651-661. Nishimura(2012): The Journal of Geological Society of Japan,
118, 278-293. Niwa, Y.(2014): The Quaternary Research, 53, 311-322. Okuno et al.(2014): Quaternary Science Reviews, 91,
42-61.
Keywords: Sanriku coast, alluvial lowland, Holocene, crustal movement

1/1

HQR23-P06

Room:Convention Hall

Time:May 24 18:15-19:30

Basin fill sediments and late Quaternary tephras under the eastern part of Aizu basin,
Northeast Japan
ISHIHARA, Takeshi1∗ ; SUZUKI, Takehiko2 ; UCHIDA, Youhei1
1

AIST, 2 Tokyo Metropolitan Univ.

Aizu Basin is one of tectonic basins aligning with north-south direction in the south part of Northeast Japan. Along the west
and east margin of the basin, the West Aizu Basin Fault Zone and the East Aizu Basin Fault Zone, active reverse faults, stretches
respectively. Geomorphic development of the basin since Miocene has been discussed by Suzuki et al. (1977), Yamamoto (2006)
and so on. Activity of both fault zones during the last a few ten thousand years was reported by Fukushima Prefecture (2002) and
AIST (2007). Kuriyama and Suzuki (2012) and Suzuki et al. (2013) detected tephras from a drilling core (AB-12-2 core, 179.08
m asl) in the western part of the basin and calculated accumulation rate of sediments since 0.2 Ma as 0.2˜0.5 m/ky. However,geological structure of the Aizu basin is still not clear because of lack of chronological studies of underground sediments in theeastern part of the basin. We drilled an all-core (GS-SOK-1 core, 175.99 m asl) with a depth of 130 m at Shiokawa, Kitakata
City, located an eastern part of the Aizu basin. In this report, we show stratigraphy of the GS-SOK-1 and detected tephras.
GS-SOK-1 core comprises alternate layers of gravel beds and fine sediment beds in total. From surface to 26 m depth silt andorganic silt beds are dominant, although thick gravel beds deposit from 26 m to 60 m. Two tephra layer are detected at 1.6˜1.8m (pumice layer) and 81.1˜81.7 m (volcanic ash layer). It is suggested that the former is Nm-NM (5.4 ka ) and the latter is atephra derived from the Sunagohara volcano. Gravel beds composed of subrounded and subrubbled pebbles in size 20-50 mm
with cobbles. Andesite cobble and tuff are included in total. Three radiocarbon ages of woods obtained from the core are as
follows: 17310-17710 cal yrBP (6.26 m depth), 17330-17730 cal yrBP (6.67 m), and 29530-30360 cal yrBP (7.64 m).
Suzuki et al. (2013) detected three tephra layer in AB-12-2 core; Nm-NM (4.1 m depth), AT (17.1 m), and Sn-MT (88.3 m).
If volcanic ash at 81.1˜81.7 m depth is compared with Sn-MT, average accumulation rate of sediments since 0.2 Ma in easternpart of the Aizu Basin is comparable with one in western part. On the other hand, GS-SOK-1 core consists of alternate layers ofgravel and fine sediment, although AB-12-2 core dominantly comprises fine sediment in total. Boring site of GS-SOK-1 is nearfans of eastern margin of the basin and volcanic-fan of Mt. Nekoma, suggesting that coarse sediments have been supplied several
time in GS-SOK-1 site.
Keywords: Aizu basin, Boring, Tephra, Underground geology, Late Quaternary

1/1

HQR23-P07

Room:Convention Hall

Time:May 24 18:15-19:30

The lower loam bed and eolian sand deposits found at Tomobe Hills, Middle Part ofIbaraki Prefecture
OOI, Shinzou1∗ ; SAIRENJI, Nobuo2 ; SUTO, Tadayasu3 ; ANDO, Hisao4
1

GSI, 2 Shirakata Elementary School, 3 Kasama City, 4 Ibaraki University

The Pleistocene Hikita and Tomobe formations are distributed in the Urizura and Tomobe hills and the Kakioka Basin,the midwestern part of Ibaraki Prefecture. Their sedimentary age remains undefined. As several tephra layers from the lower loam bed
and eolian sand deposits overlying the Tomobe Formation were found at the Tomobe Hills, we examined their correlation. Twotephras possibly correlative with ”GoP” and ”HBP”, key tephra beds of the Tama Loam in the Kanto Plain region, respectively
were included in the lower loam bed. This indicates the lower stratigraphic position for the Tomobe Formation than the Jizodo
Formation (equivalent to MIS11), Shimosa Group.
Keywords: Tomobe Hills, Eolian sand deposit, HBP Tephra, Tomobe Formation, Pleistocene

1/1

HQR23-P08

Room:Convention Hall

Time:May 24 18:15-19:30

Stratigraphic correlation of multiple coring sites in Lake Suigetsu, Fukui prefecture, central JapanYAMADA, Keitaro1∗ ; NAKAGAWA, Takeshi2 ; SAITO-KATO, Megumi3 ; STAFF, Richard4 ; KITABA, Ikuko2 ;KITAGAWA, Junko5 ; HARAGUCHI, Tsuyoshi6 ; SMITH, Victoria4 ; MCLEAN, Danielle4 ; GOTANDA, Katsuya7 ;ALBERT, Paul8 ; HYODO, Masayuki9 ; SUZUKI, Yoshiaki10 ; MATSUSHITA, Hayato11 ; YAMASAKI, Akiteru6 ;TAKEMURA, Keiji1
1

Graduate School of Science, Kyoto University, 2 Research Centre for Palaeoclimatology, Ritsumeikan University, 3 Departmentof Geology and Paleontology, National Museum of Nature and Science, 4 University of Oxford, 5 Fukui Prefectural SatoyamaSatoumi Research Institute, 6 Department of Geosciences,Graduate School of Science,Osaka City University, 7 Faculty of Polycy
Informatics, Chiba University of Commerce, 8 Swansea University, 9 Research Center for Inland Seas, Kobe University, 10 Departmentof Earth and Planetary Science, Graduate school of Science, The University of Tokyo, 11 Department of Earth and Planetary Science, Kobe University
Lake Suigetsu in Fukui prefecture, central Japan, is a tectonic lake related to the active Mikata Fault (Okada, 2004), whichmeasures 3 km east-west by 3 km north-south. The sediments of Suigetsu are important for Quaternary science, as they are
annually-laminated (varved) over the last ca.70 kyr (Nakagawa et al., 2012). The varved sediment also contains a significant
number of microscopic event layers (e.g. associated with earthquakes and floods; Schlolaut et al., 2014). Two long cores (SG93,
SG06) have previously been recovered from the centre of the lake, and an exceptionally precise age model has been established
for the cores through a combination of over 800 radiocarbon dates and high precision varve counting (Staff et al., 2011; Marshall et al., 2012; Schlolaut et al., 2012; Bronk Ramsey et al., 2012). In 2014, a new core (SG14) was recovered by the Fukui
prefectural government from a boreholes ca. 500 m to the east of the SG06 coring site. This core was obtained mainly for public
display but also provides additional samples for the scientific analysis of the event layers, tephras, palaeoclimate, palaeomagnetism, and others. High-resolution photographs of the half-core sections were taken before oxidation could take place, underprecisely controlled lighting conditions. Long soft X-ray images were subsequently taken on 1 m long giant thin-section slabs of
the core. From there, we visually correlated the SG14 core with the SG06 core using event layers, so the age model from SG06
core can be used for SG14.
The SG14 core was obtained from 4 separate boreholes (E, F, G, H) to ensure overlapping with each other. The combinedcore sections were nearly 100 m long, going ca. 30 % deeper than the SG06 core, and were almost wholly continuous except
for two cm-scale gaps. Almost all of event layers of the SG14 core, such as tephras, turbidites, could be correlated with that of
the SG06 core. On the basis of this correlation, average sedimentation rate of the SG14 core was equivalent to that of SG06;
however, the coarse layers of turbidites were different in thickness between each core. These observations support the idea thatmost of event layers spread out over wide areas of the lake bottom. Furthermore the variation in thickness between the coresprovides key geographical origin and pathways of these event layers. The upper parts of the SG14 core (0 to 44 m in composite
depth) are mainly dominated by varved sediments. Whilst the middle (44 to 65 m in composite depth) and lower parts (65 tobottom in composite depth) of the SG14 core lack laminated sediment; the middle parts primarily consist of massive sediment,
and the lower parts are composed of black-brown peat and cyclically intercalated with more inorganic grey sediments. These
stratigraphic transitions probably indicate hydrological change of the lake catchment.
References
Bronk Ramsey et al., 2012, Science, 338, 370-374.
Marshall et al., 2012, Quaternary Geochronology, 13,70-80.
Nakagawa et al., 2012, Quaternary Science Reviews, 36, 164-176.
Okada, 2004, Geomorphology of Kinki, Chugoku and Shikoku (in Japanese), University of Tokyo Press, p179-189.
Reimer et al., 2013, Radiocarbon, 55, 1869-1887.
Schlolaut et al., 2012, Quaternary Geochronology, 13, 52-69.
Schlolaut et al., 2014, Quaternary Science Reviews, 83, 157-170.
Staff et al., 2011, Radiocarbon, 53, 511-528.
Keywords: Lake Suigetsu, Event stratigraphy, Varve, Turbidite, Stratigraphic correlation

1/1

HQR23-P09

Room:Convention Hall

Time:May 24 18:15-19:30

The growth process of Oyster reefs and Diatom assemblage in Tokyo bay - focus on a
genus Amphora of diatoms
NOGUCHI, Marie1∗ ; ENDO, Kunihiko2 ; KASHIMA, Kaoru1
1

Kyushu University, 2 Nihon University

Around the tidal zone of Funabashi coast, Sanbanze, the northern Tokyo Bay, Chiba Prefecture, living oyster reefs appeared
abruptly 10 years ago. Here is sandy tidal flat near the river mouth of Edo River, where a few reefs of Crassostrea gigas ranging
100m or 200m long were formed in the lower tidal zone. Some small colonies of C. gigas have been found out at least before 20
years, however, the reason why recently the living oyster reefs appeared around Sanbanze should be clarified in relation to theenvironmental changes.
In this study, the ecosystems of the oyster reefs are composed of C. gigas, sea anemone, ragworms, seaweeds, seagrasses anddiatoms. In particular, we investigate living oyster reefs and diatoms. Oyster feed on diatoms playing a role in the base of foodchain. Our field survey checks size of reefs, habitation density in reefs and organisms around the reefs, in comparison withvarious environmental indicators by the monitoring post of the Bay.
In general only macro-benthos and fishes are treated in the ecosystems of coastal areas, though seaweeds and seagrasses areimportant to comprehend the ecosystem. Gastropods in tidal zone eat mollusks, seaweeds and seagrasses. In fact, in Sanbanze,
sea lettuces (Ulva sp., a kind of seaweeds), grows conspicuously along with seagrasses. A genus Amphora, one of the dominantdiatoms in the reefs, is living in brackish to marine water, settling on algae or plants and is useful as an important marker ofseaweeds and seagrasses in Sanbanze.
Keywords: Tokyo Bay, Oyster reefs, Diatom, Macro-benthos,, Ecosystem

1/1