HCG35-01

Room:105

Time:May 27 09:15-09:30

Separating silicate weathering effect from grain size and source rock effects on sediment
composition of Yangtze River
TADA, Ryuji1∗ ; KUBOKI, Yui1 ; ZHENG, Hongbo3 ; IRINO, Tomohisa2 ; SAITO, Keita1 ; LUO, Chao4 ;HE, Mengying3 ; WANG, Ke2 ; TSUNAZAWA, Yuya1 ; TAKAHASHI, Yoshio1
1

Graduate School of Science, the University of Tokyo, 2 Faculty of Environmental Earth Science, Hokkaido University, 3 Schoolof Geographic Science, Nanjing Normal University, 4 School of Earth Sciences and Engineering, Nanjing University
Silicate chemical weathering plays a critical role on the long-term carbon cycle and stabilizing atmospheric pCO2 by so-called
Walker feedback (a negative feedback) through neutralizing carbonic acid by dissolving Ca and Mg silicate minerals and reprecipitated as carbonates and chert (SiO2 ). Consequently, it is important to quantitatively evaluate past intensity of silicate
weathering. There are several proxies proposed for silicate weathering intensity based on chemical and/or mineral compositionof bulk sediments. However, it becomes increasingly apparent that chemical and mineral composition of bulk sediments issignificantly influenced by the difference in grain size as well as the difference in source rocks. However, none of previously
proposed proxies takes into account of both the grain size effect and source rock effect simultaneously.
We selected Yangtze River because it is one of the largest river in the world with over 250 gauge stations, the large variation in
bed rock geology among branches, and large ranges in topographic relief and climate. Thus we expect large ranges in chemical
weathering intensity and source rock types.
In this study, we used 21 river bed sediment samples and 42 suspended particulate matter (SPM) samples collected frommajor branches and throughout the main stream of the Yangtze River. We conducted grain size separation of bulk river bed
sediment samples into 3 fractions (<4µm, 4-16µm, 16-63µm). As to SPM samples, we did not conduct grain size separation
because their median diameters range from 3.5 to 10.6 µm and more than 98% of SPM is less than 100µm. We analyzed major
element composition and mineral composition of these samples by XRF and/or ICP-AES and XRD, respectively. We compare
chemical and mineral compositions of the 3 size fractions of the same samples to evaluate the grain size effect on chemistry
and mineralogy. We found sediments and SPM are basically composed of 3 components; one is Si, Na, Ti, Mn (quartz)-richcomponent representing coarser grains, another is Al, K, and Fe (clay minerals)-rich component representing finer grains, and theother is Ca and Mg (carbonate)-rich component representing dolostone and limestone fragments. Sediments from the uppermost
reaches and their branches where chemical weathering is minimal, K/Al and Fe/Al of the 3 different size fractions tend to show
similar values suggesting Al, Fe, and K are contained in the same component with the same composition that are diluted by
the coarser fraction that are dominantly composed of quartz. However, K/Al of fine fraction relative to K/Al of coarse fraction
decreases downstream with the increase in temperature and precipitation, suggesting the ration (K/Al)f /(K/Al)c ratio may reflect
the intensity of chemical weathering.
We will discuss the possibility of (K/Al)f /(K/Al)c ratio as a quantitative indicator of silicate weathering.

Keywords: chemical weathering, sediments, chemical composition, grain size effect, source rock effect, Yangtze River

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HCG35-02

Room:105

Time:May 27 09:30-09:45

ESR and TL signals in quartz in the present river sediments along with the Kurove river
YOSHIDA, Msanori1 ; TOYODA, Shin1∗ ; TAKADA, Masashi2 ; SHIMADA, Aiko3 ; NINAGAWA, Kiyotaka1
1

Faculty of Science, Okayama University of Science, 2 Nara Women’s University, 3 JEOL RESONANCE

The variations in the number of oxygen vacancies, measured as the ESR (electron spin resonance) intensity of the E1 ’ centerin quartz, and in the TL (thermoluminescence) colors in quartz of quartz of the sediments are investigated along with the Kurobe
river together with those in the bedrocks in the river reaches. The number of oxygen vacancy in quartz indicates the age of thehost rocks from which the sediments have been generated by weathering while the red TL color corresponds to volcanic origin
and blue to plutonic origin. The quantitative TL color measurements were made possible with the time-resolved 2 dimensional
TL spectroscopy system.
The number of oxygen vacancies, higher in the upper reach, gets lower in the middle, and further higher in the lower reaches
due to the inflow of the sediments originated from the younger and from the older bedrocks, respectively. The high temperature
red to low temperature blue TL ratios, higher in the upper reach, gets lower in the middle and lower reaches due to the sediments
having lower values. The change in the values along with the river flow is found to be explained by the inflow of the sediments
originated from the bedrocks around the river.
Keywords: river sediment, provenance, ESR, TL

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HCG35-03

Room:105

Time:May 27 09:45-10:00

Lead isotopic variations of fine particles discharged from rivers of Tokai area, Central
Japan
SAITOH, Yu1∗ ; TANIMIZU, Masaharu2 ; ISHIKAWA, Tsuyoshi2
1

Center for Advanced Marine Core Research, Kochi University, 2 Kochi Institute for Core Sample Research, JAMSTEC

We report lead isotopic variations of fine fraction of river sediments of the Tonankai area in order to provide the reference data
in resolving the provenance of hemipelagic sediment distributed in the Shikoku Basin. We targeted smaller particles than 10 µm.
This grain size is important because they constitute the majority of hemipelagic sediments distributed on seafloor of the Shikoku
Basin (Saitoh, 2014).
Lead isotope ratios widely differ by rivers. The most prominent contrast is recognized between the rivers draining the IzuHonshu collision zone and the others. Isotopic ratios of the former, the Sagami, Sakawa, and Kano rivers are low (206 Pb/204 Pb:
18.15-18.3; 207 Pb/204 Pb: 15.55-15.59; 208 Pb/204 Pb: 38.1-38.4), while those of the latter are higher (206 Pb/204 Pb: 18.46-18.66;
207
Pb/204 Pb: 15.59-15.63; 208 Pb/204 Pb: 38.6-38.9) (Figure). The low ratios of the former are supposed to be the results of thecontribution from the mafic rocks distributed around the collision zone. Contribution from the sedimentary rocks of accretionary
complexes distributed in the watersheds must increase the isotopic ratios of the other rivers. Minor isotopic differences aresupposed to be dependent on the age of accretionary comprex and types of other rocks distributed in watershed of each river.
Isotopic comparison with these river sediments suggests that the sediments of the Shikou Basin deposited after 3Ma are mainly
contributed from the Fuji, Abe, and Tenryu rivers.
Sr-Nd isotope ratios of river sediments will be also shown and discussed.
Reference
Saitoh, Y., 2014. Data report: grain size distribution of the late Cenozoic hemipelagic mud from Site C0011. In Henry, P.,
Kanamatsu, T., Moe, K., and the Expedition 333 Scientists, Proceedings of the Integrated Ocean Drilling Program 333: Tokyo(Integrated Ocean Drilling Program Management International, Inc.).

Keywords: Pb isotope ratios, Sr-Nd isotope ratios, river sediments, hemipelagic sediments, Shikoku Basin

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HCG35-04

Room:105

Time:May 27 10:00-10:15

Grain and chemical composition of coastal sand in Kanto and adjacent region
HAGIYA, Hiroshi1∗ ; ISHII, Atsuko2 ; SEKI, Masayuki1 ; HORI, Ayumi1
1Tokyo City University, 2 Toppan Printing Co. Ltd.

Grain composition and chemical composition of beach sand, over 200 samples collected from Southern Abukuma region,
Choshi region, Kujukuri region, Shonan region and West Suruga-Bay region, had analysed.
The composition of sand had wide variety in Kanto and adjacent region, and also show areal differences in each coast, causedby sand supply from river system and coastal current differenciation.
Rock fragment dominates in both Shonan and West Suruga-Bay coast, but Shona sand consist of mainly volcaniclastic fragment, while West Suruga-Bay sand consist of sedimentary rocks origin fragment, which made in accretionary process in subduction zone. Trace element composition shows also differences between two coast in sand grain origin.
We will discuss about the importance of grain and chemical composition analysis of recent coastal sands, not only in the fieldof coastal engineering, but also in earth science, in the context of tectonic setting analysis of geological time scale.
Keywords: beach sand, grain composition, chemical composition, trace element, tectnic setting, erosion

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HCG35-05

Room:105

Time:May 27 10:15-10:30

Variation of source rock assemblage recorded in the Tokiguchi Porcelain Clay Formation
HATANO, Nozomi1 ; YOSHIDA, Kohki2∗ ; SASAO, Eiji3 ; ADACHI, Yoshiko4 ; IWANO, Hideki5 ;DANHARA, Toru5
1
3

Division of Science and Technology, Graduated School of Shinshu University, 2 Department of Geology, Shinshu University,
Japan Atomic Energy Agency, 4 Faculty of Science, Niigata University, 5 Kyoto Fission-Track Co.Ltd

The Miocene Tokiguchi Porcelain Clay Formation consists mainly of muddy sediments, which were deposited in the tectonical controlled small inland basin in the southern part of the Gifu Prefecture, central Japan (Nakayama and Todo Collaborative
Research Group, 1989). The depositional age of the formation is designated to Middle Miocene (approximately 10 Ma) on thebasis of the yielding of Penus trifolia (Miki, 1939) and radiometric ages of tuffaceous sediments (Yoshida et al., 1997).
The sedimentological studies after 1980’s revealed the depositional environments and detail of the sedimentary basin (ex.
Nakayama and Todo Collaborative Research Group, 1989). Recently, paleosol horizons are reported from this formation (Hatano
and Yoshida, 2014).
This research focuses the U-Pb radiometric ages of detrital zircon grains in the sandy sediments in this formation in order toclarify the provenance variations by radiometric ages. Additionally bulk rock assemblage of the hinterland was estimated by
the REE chemical composition of the muddy sediments to search the source rock assemblage. The detrital zircon grains were
sampled from Hishiya and Nakayama Mines, which are separated into 1 km distance, in Tajimi and Toki Cities respectively. As
a result, the zircon grains sampled from the Hishiya Mine mainly indicate 70- 80 Ma, accompanied with zircons showing 200,
1700, 1900 Ma, while the zircons from the Nakayama Mine concentrate mainly 12-15 Ma with small amount of zircons in 1700,
1800 and 2900 Ma. REE composition of the muddy sediments indicates various source rocks in the hinterland including basic,
intermediate and felsic rocks.
The Late Cretaceous-Early Paleogene radiometric ages were reported from the basement igneous rocks, Inagawa Granite (5686Ma; Shibata et al., 1962; Suzuki and Adachi, 1998), Toki Granite (68-72Ma; Shibata and Ishihara, 1979; Suzuki and Adachi,
1998), Nohi Rhyolite (58-85Ma; Yamada and Koido, 2005), distributed around the sedimentary basin of the Tokiguchi Porcelain
Clay Formation. Also the detrital zircons yielding Early-Middle Miocene ages are reported from the Early-Middle Miocene
Mizunami Group (Sasao et al., 2006, 2011). Thus, the zircon group showing 70-80 Ma is interpreted to be originate from basement rocks. The group with 11-15 Ma zircons was possibly derived the Mizunami Group sediments. The zircon grains with
Archaean - Proterozoic ages imply the derivation from the Jurassic Mino Terrane.
Though the Tokiguchi Porcelain Clay Formation in above two mines were deposited in the same sedimentary basin, the age
assemblage of detrital zircons shows significant difference which implies provenance variation. Also REE geochemistry is indicative of various source rock assemblage in the hinterland. These permit an inference that the change of river catchment area
and interfingering deposition by the different river discharge made the difference of provenance records.
This study was carried out under a contract with METI (Ministry of Economy, Trade and Industry) as part of its R&D supporting program for developing geological disposal technology.
Reference
Hatano and Yoshida, 2014, Abst. 121th Ann. Meet. Geol. Soc. Japan, 252. Miki, 1939, Bot. Mag. Tokyo, 53, 239-246.
Nakayama and Todo Collaborative Research Group, 1989, Monograph Assoc. Geol. Collaboration Japan, 36, 237-246. Sasao etal., 2006, Jour. Geol. Soc. Japan, 112, 459-468. Sasao et al., 20011, Jour. Geol. Soc. Japan, 117, 476-481. Shibata et al., 1962,
Bull. Geol. Surv. Japan, 13, 317-320. Shibata and Ishihara, 1979, Geochem. Jour., 13, 113-119. Suzuki and Adachi, 1998, Jour.
Metamorphic Geol., 16, 23-37. Yamada and Koido, 2005, Monograph Assoc. Geol. Collaboration Japan, 53, 15-28. Yoshida etal., 1997, Abst. Japan Earth Planet. Joint Meet., 584.

Keywords: Miocene, Chemical Weathering

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HCG35-06

Room:105

Time:May 27 10:30-10:45

Geochemistry and Clay mineralogy of Paleosols in the middle Miocene Tokiguchi Porcelain Clay Formation
HATANO, Nozomi1∗ ; YOSHIDA, Kohki2 ; ADACHI, Yoshiko3
13

Division of Science and Technology, Graduated School of Shinshu University, 2 Development of Geology, Shinshu University,
Faculty of Science, Niigata University

The middle Miocene Tokiguchi Porcelain Clay Formation is fluvial deposits distributed in Aichi to south-eastern Gifu Prefecture (Akamine, 1954; Nakayama and Todo Collaborative Research Group, 1989). This formation is mainly composed of clay-siltwith lignite and that is known as a high quality resource of ceramics (Fujii, 1967). Most previous studies had focused on the clay
mineral composition and the parent materials so as to imply the mechanism and the timing of genesis of clay minerals (ex. Fujii,
1968; Tanemura, 1964). In general, clay mineral composition of sediments, however, is affected by parent materials, sorting ofspecified minerals during erosion, transportation and deposition and the chemical weathering after the deposition. The Tokiguchi
Porcelain Clay Formation includes apparent paleosols that were formed by the physical, biological and chemical modifications of
sediments and exposed at the earth surface. The paleosol horizons, thus, provide detailed information related to paleoweathering
regimes. In this study, accordingly, we aim to clarify the relation among geochemistry, clay mineral composition, sedimentationand development of the paleosols in the Tokiguchi Porcelain Clay Formation.
The sedimentological measuring was performed in three mines, where were distributed within a radius of 5 km, across Tajimi
to Toki Cities in Gifu Prefecture. The formation, besides, exposes as 15 to 30 m thick succession in these mines.
The sedimentary facies associations indicate that depositional environments was mainly in lake, swamp and marsh. Furthermore, approximately 20 paleosol horizons can be recognized in each mine. These paleosol horizons are characterized by various
pedogenic features, such as root fossils over 150 cm in length, apparent soil horizons which include A, B and C horizons andmicrofabric of clay minerals.
The clay mineral assemblage of fine deposits is composed of almost kaolinite, expandable clay minerals, mica clay mineraland chlorite. There are no significant relationship between the clay mineral assemblage and the soil horizons, but the clay mineral
assemblage is correlatable to the grain size of the sediments.
Geochemical approach indicates the variation of the parent materials in each horizon. In some horizons, the chondritenormalized REE patterns show significant negative Eu anomaly and enrichment of LREE, which mainly suggest the provenanceof felsic parent rocks. Whereas, in the other horizons, the REE patterns show slight negative Eu anomaly and gentle slope of
LREE. The sediments of these horizons are characterized by the high expandable clay minerals/kaolinite ratio and yielding chlorite. In addition, the chemistry and clay mineral composition suggest the major provenance of mafic parent rocks.
The Chemical Index of Alteration (CIA index; Nesbitt and Young, 1982, 1984) shows high chemical weathering degree as awhole clay-silt samples from 88 to 95. In the surface soil horizons, furthermore, the paleoweathering ratios are higher than thatin the sub-surface soil horizons. Thus, the chemical paleoweathering had been progressed in the soils after the deposition.
Though, the geochemistry shows the provenance variety in each horizon of the Tokiguchi Porcelain Clay formation, intense
chemical weathering had masked provenance variety. In consequence those results suggest the progression of paleoweatheringon the hinterland and after the deposition in the Tokiguchi Porcelain Clay Formation.
Reference
Akamine, 1954, Misc. Rep. Res. Inst. Natural Resources, 34, 25-39.
Nakayama and Todo Collaborative Research Group, 1989, Monograph Assoc. Geol. Collaboration Japan, 36, 237-246.
Fujii, 1968, Rep. Geol. Surv. Japan, 230, 1-15.
Fujii, 1967, Bull. Geol. Surv. Japan, 18, 1-19.
Nesbitt and Young, 1982, Nature, 299, 715-717.
Nesbitt and Young, 1984, Geochimica et Cosmochimica Acta, 48, 1523-1534.
Tanemura, 1964, Rep. Geol. Surv. Japan, 203, 1-40.
Keywords: paleosol, chemical weathering, Miocene, chemical composition, rare earth element, clay mineral composition

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HCG35-07

Room:105

Time:May 27 11:00-11:15

Cyclostratigraphic analysis of the Middle Triassic bedded chert sequences in Southwest
Japan
SODA, Katsuhito1∗ ; ONOUE, Tetsuji1 ; IKEDA, Masayuki2
1

Kumamoto Univ., 2 Shizuoka Univ.

Milankovitch cycle recorded in sedimentary rocks provides a high resolution and precision astronomical time scale throughout
the Earth history. Bedded chert sequences of the Jurassic accretionary complexes in Southwest Japan have a potential for thetemplate of the early Mesozoic astronomical time scale. Although astronomically paced sedimentary rhythm of the Triassic
bedded chert sequence was detected in the Inuyama area of the Mino Belt, central Japan (Ikeda et al., 2010), the validity requires
detailed stratigraphic correlations to other Triassic bedded chert sequences in Japan.
In this study, we investigated the sedimentary cycle of the Middle Triassic (Anisian) bedded chert sequence in the Tsukumi
area of the Chichibu Belt, Southwest Japan. The study section is located at the Ajiro Island in the Tsukumi area of the Chichibu
Belt, Southwest Japan. The depositional age for the bedded chert sequence is Middle Triassic (Anisian) based on radiolarian bio
and magnetostratigraphy (Uno et al., 2012).
The average duration of a chert and shale couplet in the Middle Triassic bedded chert of the Tsukumi area is ca. 10 kyr. Thisduration is inconsistent with the ca. 20 kyr duration of the precession cycle during the Triassic, which was confirmed by estimatedaverage duration of a chert and shale couplet in the Triassic bedded chert of the Inuyama area. The dominant cycles in a bed
number series of thickness variations in the Middle Triassic chert beds show approximately 2, 5, 10, 40, 200, 300 and 400 beds
cycles. Given that the average duration of one chert and shale couplet is ca. 10 kyr, these cycles correspond to approximately
20, 50, 100, 400, 2000, 3000 and 4000 kyr periodicities. The periodicities of the Tsukumi chert are consistent with those of theInuyama chert (approximately 40, 60, 100, 140, 240, 400 and 4000 kyr).
Previous palaeomagnetic studies have revealed that the Middle Triassic bedded chert in the Ajiro Island section were depositedin the equatorial region, whereas the deposition of the Inuyama chert occur at relatively higher latitude. If the interpretation thatrhythmical alternations of chert and shale beds are paced by precession and eccentricity cycles is valid, the average durationof a chet and shale couplet from the Tsukumi area might reflect the semiprecession cycle (ca. 10 kyr) in the equator area
caused by biannual passage of the Sun. However, the phases of the bedded chert thicknesses in a bed number series show noclear relationships between Tsukumi and Inuyma areas despite bio and magnetostratigraphic correlation. Further stratigraphic
analyses will be required to estimate the paleolatitudinally dependent patterns in the cyclicities of the Triassic bedded chert
sequences in Japan.

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HCG35-08

Room:105

Time:May 27 11:15-11:30

Seismic geomorphology of Miocene shelf-to-slope depositional system in the southeastern part of the Tsushima Basin
EGAWA, Kosuke1∗ ; SAKATA, Genki1 ; MIYAMOTO, Hiroki1 ; ABE, Yosuke1 ; MATSUURA, Shinji1 ;IMAMURA, Tetsumi1 ; HARA, Takateru1 ; AKUTSU, Toru1
1

INPEX Corporation

We report three-dimensional (3-D) seismic geomorphologic features of a shelf-to-slope depositional system in the southeasternpart of the Tsushima Basin, offshore Southwest Japan, by using the 3-D seismic survey dataset of Shimane-Yamaguchi-oki. The
studied Miocene succession presents seismic facies characterized by incised valleys/channels and subsequent multiple stacked
slope channels from shelf to slope, with well-developed clinoform reflections. Such seismic aspects strongly suggest the development of a prograding delta system during Miocene time similar to offshore South Korea.
Keywords: Seismic geomorphology, 3-D seismic survey, Tsushima Basin, Shelf-to-slope depositional system, Miocene

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HCG35-09

Room:105

Time:May 27 11:30-11:45

Developing process-oriented studies of tsunami-induced erosion and deposition, and morphological changes: A brief review
SUGAWARA, Daisuke1∗ ; NARUSE, Hajime2
1

Tohoku University, 2 Kyoto University

Tsunamis are capable of eroding huge amount of sediments, depositing them everywhere in the impacted areas and modifying
the coastal morphology. Decrypting geological records of tsunamis as well as modeling their sedimentary processes is crucial
for providing information for improved hazard assessment. In addition, geological and sedimentological researches may lead us
to comprehensive understanding of the linkage of sedimentary process between land and sea (Goto et al., 2014), and clarifying
long-term changes in coastal morphology and environments regarding the effects from infrequent large-scale tsunamis.
What information of the tsunami is reflected to its deposits depends on the local settings and dynamics of the tsunami waves.
For example, eyewitness accounts suggested that the second wave of the 2011 Tohoku tsunami brought the massive marine sediments onto the head of Samenoura Bay, southern Sanriku Coast. The first wave, which had an equivalent height to the second
wave, did not contributed to the formation of the tsunami deposit (Sugawara et al., 2014a). In this case, no information for the
first wave can be extracted from the tsunami deposit.
Understandings (and sometimes insights as well) on the processes of the tsunami wave, flow and sediment transport are indispensable to derive interpretations of the deposits that is consistent with the tsunami behavior. Numerical modeling is capable ofcapturing part of the dynamics of tsunami sedimentation. Along with perspectives of local morphology and sedimentary environment, the modeling may provide aids to interpret the tsunami deposits and tsunami-induced morphological changes.
Our increasing knowledge on tsunami deposits is founded on the various kinds of massive datasets since the beginning of theresearch field, in particular after the 2004 Indian Ocean and the 2011 Tohoku Tsunamis. Numerical studies of tsunami sedimenttransport are also founded on the dataset, and these studies brought improved understandings on the tsunami sedimentation.
In the case of the 2011 Tohoku Tsunami in Sendai Plain, geological data for the lack of marine signature from the onshore
tsunami deposit and the characteristic deposition patterns were explained by the numerical modeling of tsunami transport ofsandy sediments (Sugawara et al., 2014b). Tsunami deposits sometimes share their sedimentological characteristics with turbidites. Similarities in terms of a coupled hydrodynamic-transport process between onshore tsunami flooding and submarine
self-accelerating turbidity current are found recently and they have been investigated using numerical approaches (Naruse et al.,2014).
Collaboration of observation and modeling are the key for integrated understanding of tsunami erosion, deposition and morphological change. Process-oriented researches may contribute to depict the dynamics of tsunami sedimentation and to make
improved criteria to interpret tsunami deposits.

Keywords: Tsunami deposit, sediment transport, numerical modeling

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HCG35-10

Room:105

Time:May 27 11:45-12:00

Palaeoseismic signals in coastal dune ridge systems
GOFF, James1∗ ; SUGAWARA, Daisuke2
1

University of New South Wales, Australia, 2 IRIDeS, Tohoku University

Palaeoseismic research in regions adjacent to active fault zones has traditionally been concerned with identifying geologicalor geomorphological features associated with the immediate effects of past earthquakes, such as tsunamis, uplift or subsidence,with the aim of estimating earthquake magnitude and/or frequency. In a palaeoseismic context, coastal dune ridge systems areinvariably used to infer relative sea level change, be it by uplift or subsidence. However, on a catchment-wide basis, research
has linked a sequence of environmental changes such as forest disturbance, landslides, river aggradation and rapid coastal dunebuilding as geomorphological after-effects of large earthquakes (Figure 1). In this model large pulses of sediment created byco-seismic landsliding in the upper catchment are moved rapidly to the coast where they leave a clear signature in the landscape.
Coarser sediments form an aggradation surfaces and finer sediments form a new coastal dune or beach ridge. Coastal dune ridge
systems are not exclusively associated with seismically active areas, but where they do occur in such places their potential use as
palaeoseismic indicators is often ignored. Data are presented from sites in both New Zealand and Japan to illustrate the concept.
First, a well dated suite of coastal dune ridge sequences in SW New Zealand are shown to be linked by a series of geomorphological processes to large ruptures of the regionally significant Alpine fault (Wells and Goff, 2006; 2007). These fine resolution
chronological sequences were achieved using the ages of trees from the ancient forest still growing there. A time lag of 10-50
years between earthquake and dune ridge formation attests to the short sediment transport distance from the mountains to thecoast (˜50 km) coupled with high annual rainfall. Second, these data are contrasted with evidence from SE New Zealand where alonger sediment transport distance from the mountains to the coast (˜150 km) coupled with lower annual rainfall causes a time lagof 150-200 years between earthquake and dune ridge formation (McFadgen and Goff, 2005). Differences in coastal configuration and a lack of native forest chronology complicate event chronologies but additional geomorphological indicators and human
responses enhance interpretations. Third, we investigate beach ridges of northern Honshu with a focus on the Sendai Plain wherea study carried out following the 2011 Tohoku-oki earthquake and tsunami reveal a regional picture of the seismic driving ofbeach ridge formation. More work needs to be done but the initial results are both exciting and have significant implications forunderstand the palaeoseismic and palaeotsunami record for the region.

References:Goff, J. and McFadgen, B.G. (2002) Seismic driving of nationwide changes in geomorphology and prehistoric settlement ? a
15th Century New Zealand example. Quaternary Science Reviews, 21, 2229-2236.
Goff, J. and Sugawara, D. (2014) Seismic driving of sand beach ridge formation in northern Honshu? Japan. Marine Geology,
358, 138-149.
McFadgen, B.G. and Goff, J. (2005) An earth systems approach to understanding the tectonic and cultural landscapes of linked
marine embayments: Avon-Heathcote Estuary (Ihutai) and Lake Ellesmere (Waihora), New Zealand. Journal of Quaternary Science, 20, 227-237.
Wells, A. and Goff, J. (2007) Coastal dunes in Westland, New Zealand, provide a record of paleoseismic activity on the Alpine
fault. Geology, 35, 731-734.
Wells, A. and Goff, J. (2006) Coastal dune ridge systems as chronological markers of paleoseismic activity ? a 650 year record
from southwest New Zealand. The Holocene, 16, 543-550.

Figure 1: The seismic cascade of physical and human environmental responses to giant earthquakes (after Goff and McFadgen,2002; Goff and Sugawara, 2014).

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HCG35-10

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Time:May 27 11:45-12:00

Keywords: Earthquakes, Tsunamis, Dune ridges, Landslides, Rivers, Geomorphology

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HCG35-11

Room:105

Time:May 27 12:00-12:15

Equilibrium condition for high-concentration turbidity currents
NARUSE, Hajime1∗
1

Graduate School of Science, Kyoto University

This research theoretically explore formative conditions and characteristics of high-concentration turbidity current. Generally,it has been suggested that suspended load even in very high-velocity flows such as tsunamis or turbidity currents cannot exceed
1-5 vol.%. This is because density stratification due to suspended load inhibit turbulence in flows.
However, it was revealed that flow can attain very high concentration (˜30%) of suspension because of hindered settling. Whencalculation starts from very high-concentration and high turbulent kinetic energy, positive feedback between sediemnt entrainment from a bed and hindered settling occurs, and finally flows reach the equilibrium condition in which suspended load isaround 30 vol.%. This equilibrium condition requires (1) small grain-size (<200 micron meter), very high initial concentration(>20 vol.%), (3) high flow velocity (>5 m/s).
The origin of two types of turbidity currents, i.e. low- and high-concentration flows, has been subject to debate for sedimentologists. This research implies that two types of flows are generated from different initial conditions. For example, tsunamigenerated turbidity currents are supposed to be low-concentration initally, so that they cannot increase their concentration even
if the self-acceleration mechanism works. On the other hand, turbidity currents generated by subaqueous debris-flows are supposed to have very high concentration of suspension, and therefore they may sustain their high-energy and concentration for long
distance.
Keywords: turbidity current, hindered settling, turbulence, suspension, turbidite

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HCG35-12

Room:105

Time:May 27 12:15-12:30

Modeling runout and deposition of dense granular flows and its application to pyroclastic
density currents in nature
MAENO, Fukashi1∗
1

Earthquake Research Institute, the University of Tokyo

Constraining physical parameters of pyroclastic density currents generated by collapsing of lava domes or eruption columns
is important to assess volcanic processes and hazards, but is a significant challenge because the mechanics of pyroclastic grains
and their interactions are incompletely understood. One approach has been to exploit the thinness of the flows relative to theirlength by employing a depth-averaged description. A key issue is the granular friction law that is introduced into the models.
Recent laboratory studies on granular flows suggest that rheology can be described by friction coefficients. Variation of thefriction coefficients related to physical parameters such as shear rate and pressure is captured through dimensionless numbers(e.g., Maeno et al., 2013). Under the shallow water assumption how well the friction models work remains unclear when applied
to pyroclastic density currents in nature. In this presentation, I will introduce the shallow water model of granular flows withdifferent types of granular friction laws, and discuss their application to natural system and related issues, taking a case study for
Soufriere Hills volcano, Montserrat, Caribbean.
Recent dome collapse events at Soufriere Hills volcano provide good examples to study the dynamics of pyroclastic density
currents and to examine granular flow models, because of abundant geological and geophysical data. Here the 20 May 2006 lava
dome collapse and resultant deposit are focused. The total collapse volume of the 2006 event was 97 Mm3 , of which about half
was dense granular components (Trovimovs et al., 2012). The seismograms showed a prolonged buildup of increasingly large
block and ash flows lasting ˜90 min. The most intense phase that produced the main deposit occurred in 35 min with two marked
peaks. Based on the collapsed volume and the duration of seismicity, an average collapse rate can be estimated to be 4.7∗104
m3 /s. On the other hand, the submarine deposit is characterized by an elongated shape in flow direction and by levee-like facies.
The deposit shape was very different from that produced in the 2003 event where collapsed materials 170 M m3 was released
in 2.6 hours with an average collapse rate 1.8∗104 m3 /s, and the shape of proximal submarine deposit was characterized bysemicylindrical, steep-sided lobes.
To investigate the factors controlling the shape of the deposit in 2006, the 2D shallow water model of granular flows withdifferent types of Coulomb-type friction models is applied to the terrain of the Soufriere Hills. One had a constant friction
coefficient, and another had a friction coefficient that depends upon the dimensionless inertial number (I ) of the motion. For
source condition, a constant mass or a line source with a flux function were used. Parameter studies were carried out withinpossible ranges of parameters such as volume, grain-size, and friction angles. When the I -dependent friction model was appliedwith a flux function and specific values of the parameters were used, the characteristics of deposit shape can be reproduced. The
I -dependent friction model works better after the flow passing a slope break point where slope angle is equal to the friction angle
at zero shear rate. Our results suggest that coupling effects of discharge rates, slope and granular friction properties may explain
the different shapes of the deposits produced by dome collapse events at Soufriere Hills volcano.
References: Maeno, F. et al. (2013) Physics of Fluids, 25, 023302, doi:10.1063/1.4792707, Trofimovs, J. et al. (2012) Bull.
Volcanol., 74, 391-405.
Keywords: pyroclastic density currents, granular flow, modeling, shallow water theory

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HCG35-13

Room:105

Time:May 27 14:15-14:30

Distribution and its sedimentary process of river terrace deposits along the middle Kaligandaki, central Nepal
YOSHIDA, Takahiro1∗ ; SUGANUMA, Yusuke2 ; SAKAI, Tetsuya3
1

SOKENDAI University, School of Multidisciplinary Sciences, 2 National Institute of Polar Research, 3 Shimane University, Interdisciplinary Faculty of Science and Engineering”Kali Gandaki”is the river runs through the Himalayas from Tibetan plateau to Indian plain. A number of river terraces
are distributed along the middle part of the Kali Gandaki. Recent researches reported that catastrophic events such as glaciallake outburst flood (GLOF) and large-scale slope failure have strongly affected developments of river terraces in the Himalayas(Takada,1992. Schwanghart et al,2014). The river terraces along the middle Kali Gandaki have also been thought to be composed of GLOF deposits (Yoshida & Upreti, 2014). Sharma (1980), Yamanaka (1982) originally classified the river terraces
based on aerial photo interpretation. Although these pioneering studies have contributed greatly to our understanding of the geomorphological development of the terraces, the classification needed to be examined by using modern highly-accurate altitude
measurements, such as GPS. In addition, lithofacies of the river terrace deposits have not been described, which hampers understanding of the depositional processes of the terraces and its origin. Therefore, we carried out re-classification of the terraces
and sedimentological description of the terrace deposits along the middle Kali Gandaki (Beni ˜Phalebas) to understand theirdepositional process and origin. Here we report three achievements as follows.
1)Based on detailing geomorphological analysis by using GIS software coupled with absolute altitude measurements (GPS),the river terraces along the middle Kali Gandaki are re-classified.
2)Lithofacies of the terrace deposits, which were originally described as a single gravel bed, are subdivided into six different
types. They often include high-density flow deposits such as debris flow or mud flow.
3)At the confluence of rivers, Iithofacies of the river terraces laterally change to be finer from the mainstream to tributaries. It
indicates a rapid accumulation of the river terrace deposits along the mainstream of Kali Gandaki. These suggest that the geomorphological development of this area was (partly) affected by the GLOF events. We will focus on high-density flow deposits,
and consider their depositional process, origin, and depositional age.

Keywords: Himalayas, Kaligandaki, River terrace

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HCG35-14

Room:105

Time:May 27 14:30-14:45

Late Quaternary river terrace development and estimation of vertical crustal movement
along branches of the Tone River
MORITA, Yasuhiko1∗ ; SUGAI, Toshihiko2
1

Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 2 Department of Natural
Environment, Graduate School of Frontier Sciences, The University of Tokyo

Introduction
Vertical crustal movement can be estimated by seismologic, geodetic, geomorpholoical and geological approaches in short order. For prehistorical crustal movement, estimation based on geomorphological and geological evidence is valid. While marine
terraces have been used in coastal areas (Koike and Machida, 2001), it is necessary to use a different method in inland areas.
When similar longitudinal profiles of the river floor are made under similar climate conditions and similar sea levels, relative
height between the two terrace levels formed in two successive full-glacial periods may indicates vertical crustal movement occurred in between the two full-glacial periods. This method is called TT (Terrace to Terrace) method (Yoshiyama and Yanagida,1992). The accuracy of the crustal movement evaluation is considered to be reduced. For these reasons, there is a need for basic
study to know the applicable accuracy and limitations of the TT method.
Purpose of study
Tajikara(2000) estimates the crustal movement in Tohoku region based on the TT method. There is also a comprehensively
study classified the longitudinal profiles, which is an important element in our study, of the many rivers of Japan as an approximation function form (Honda and Sugai, 2011). By combining these results with this study, it is possible to analogize the tendency
of longitudinal profiles change which is not yet fully understood in inland. The purpose of this study is to expand the range towhich we can apply TT method in inland.
Method of study
In this study, we conducted a survey in the Kanna river area where fluvial terrace levels have been preserved well. First we
made a landform classification by aerial photo interpretation, and we measured relative height of terrace surface using a simple
laser surveying instrument. The major elemental composition of the wind stratification such tephra covering the terraces wereanalyzed using SEM EDS. We measured the relative height of fluvial terraces using 1: 25000 topographic maps of contour interval 10 m and 1: 2500 by the city planning map of contour interval 2 m along with laser meter, and we have created longitudinal
profiles of the Kanna River bed and terrace levels.
Results and discussion
In the middle terrace of downstream region, AT tephra with age of 29ka was observed. Although marker tephras from thelower layer was not detected, the middle terrace probably can be correlated with MIS 6 because of such several conditions as
gravel weathering below the layer and dissected terrace plain while the lower terrace has developed on wide area and hardly
dissected. TT value is 19-29 m between MIS 6 and MIS 2, and average of crustal movement can be estimated to be about 0.14
- 0.22 mm/yr. In upstream region fluvial terraces can be classified into three levels in Sanchu area. The highest terrace possibly
was formed in MIS 12. We made series of sampling in the upper terraces outcrop, and tried to determine the age of older (wesuppose) than the last glacial age terraces by the tephra analysis.
References
Koike and Machida, 2001, The Atlas of Marine Terrace in Japan, University of Tokyo Press.
Yoshiyama and Yanagida, 1992, Uplift Rates Estimated from Relative Heights of Fluvial Terrace Surfaces and Valley Bottoms,
Journal of Geography 104, p809-826.
Yasue and Tajikara, et al, 2011, Estimation method of uplift during late Quaternary in an inland area: Case study of fluvial
terraces along Kaburagawa river and Tokigawa river, Journal of Nuclear Fuel Cycle and Environment 18(2), p51-61.
Dury, G. H., 1959, The Face of Earth, Penguin Books, Hamondsworth, 251p.
Kaizuka, 1977, The Topography of Japan: Characteristics and Origin, Iwanami shinsho, p163-169; 222-230.
Tajikara, 2000, Chikyu monthly symposium 31, p173-181.
Honda and Sugai, 2011, Late Quaternary Change in the Longitudinal Profiles of Rivers in Japan, Transactions of Japanese
Geomorphological Union 32(3), 293-315.

Keywords: fluvial terrace, TT method, crustal movement, tephra, longitudinal profile, Kanna River

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HCG35-15

Room:105

Time:May 27 14:45-15:00

A numerical model for predicting alluvial cover in clast-rough and clast-smooth bedrock
channelINOUE, Takuya1∗ ; IZUMI, Norihiro2 ; SHIMIZU, Yasuyuki2 ; PARKER, Gary3
1

Civil engineering research institute for cold regions, 2 Faculty of Engineering, Hokkaido University, 3 University of Illinois at
Urbana-Champaign
The areal fraction of bedrock covered by alluvium is typically modeled as a function of relative sediment flux (sedimentsupply rate over bedload transport capacity), yet little is known about how the roughness of the underlying bedrock affects theextent of alluvial cover. In this study, we performed flume experiments under varied sediment supply rates and bedrock surface
topographies. We then developed a two-dimensional numerical model for predicting the cover fraction in consideration of therelative roughness (bedrock hydraulic-roughness over grain size), and tested the sensitivity of the model to changes in bedrock
relative roughness and relative sediment flux.
The numerical results show that: 1) the cover fraction is smaller when the bedrock relative roughness is smaller; 2) when
bedrock roughness is larger than alluvial roughness (clast-rough bedrock), the cover fraction gradually increases with sedimentsupply; 3) in the case of clast-rough bedrock with high sediment supply, mixed alluvial-bedrock alternate bars form, and ameandering thread of alluvial material migrates downstream; 4) when bedrock roughness is smaller than alluvial roughness(clast-smooth bedrock), a fully exposed bedrock channel requires a relatively large sediment supply before any alluvial patch
is formed, and as supply increases, rapidly transitions to a fully alluvial channel; 5) in the case of clast-smooth bedrock, thetransition between a fully exposed bedrock channel and a fully alluvial channel has hysteresis.
Keywords: Bedrock river, Fluvial geomorphology, Modeling, Sediment transport

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HCG35-P01

Room:Convention Hall

Time:May 27 18:15-19:30

Automatic identification and statistical characteristics of annual layers in stalagmites
SASAKI, Hana1∗ ; ISHIHARA, Yoshiro2 ; YOSHIMURA, Kazuhisa3 ; ONISHI, Yuri2
1

Graduate School of Science, Fukuoka University, 2 Department of Earth System Science, Fukuoka University, 3 Faculty of
Sciences, Kyushu University
Records of chemical and isotopic compositions of stalagmites, such as Mg/Ca, and carbon isotope ratios, provide various
kinds of paleoenvironmental details, for instance, information related to changes in vegetation and solar cycles. Annual layers
recognized in stalagmites are also used as an age proxy for paleoenvironmental information. These layers are mainly formed byannual changes in the impure materials incorporated within the layers, and in some layers, it is possible to use ultraviolet rays toobserve fluorescent impurity materials such as fulvic acids. It has been concluded that the process of formation of annual layers
in stalagmites is deeply related to the following: the sedimentation rate affected by the rate of dripping water, the calcium ion
concentration in that water, the form of the stalagmite, the carbon dioxide concentration in caves, and the surface environmental
changes affecting fulvic acid production. However, a number of unsolved problems remain related to the ways in which thesefactors affect the thickness of an individual annual layer and the fluorescence intensity.
When using annual layers in stalagmites as an age proxy, the sedimentation rate during specific intervals is estimated fromthe average thicknesses of these layers. If the sample includes indistinct layers, their adjacent upper or lower section data areused. However, the frequent use of microscopes in performing annual layer counts and thickness measurements in stalagmites is
associated with problems of reproducibility. Therefore, establishment of a method for objectively and quantitatively measuring
annual layers in stalagmites that includes statistical analysis, as is strongly suggested in paleoenvironmental studies, would
improve data reliability. In this study, an automatic measuring method developed for lacustrine varved diatomites was applied toannual layers in stalagmites, and statistical analyses were performed on the measurement results.
Annual layers in stalagmites were photographed using a fluorescence microscope. Identification and measurement of annual
layers in digital images were performed using the method proposed by Sasaki et al. (in press). The procedure used for identifying
and measuring annual layers using this method was as follows: (1) the gray values in the images were smoothed, and the change
rates of these values were calculated, (2) the median values of the smoothed gray values in a moving window were calculated, (3)the annual layers were identified based on combinations of the maximum change rate in (1) and the median value in (2). After
identification of the annual layers, their thicknesses were measured at boundaries of the identified layers.
The results suggest that the automatic identification method developed for lacustrine deposits can be applied to the annual
layers of stalagmites. An asymmetrical stratigraphic variation of the fluorescence intensity, which can be related to the formation
process of the layer, was observed within a layer of stalagmites. The thicknesses of the layers and their average fluorescenceintensities have a wide range of values, even in the short term, so their time series fluctuate considerably. In an example of annual
layers in a stalagmite obtained in Ryuo-do Cave in Saikai City, Nagasaki Prefecture on Kyushu Island, the following was found:a wide range of the normal thickness frequency distribution or an approximately lognormal thickness frequency distribution witha range of approximately 50-200 micrometer; an increasing fluorescence intensity in each layer from the lower to upper part;and a fluctuation of the fluorescence intensity in layers unrelated to the fluctuation of the layer thicknesses. The results suggestthat the formation process of the annual layers is highly affected by the cave environment, and thus further study involving direct
observations of the formation process of annual layers on stalagmites is indicated.
Keywords: annual layer, image analysis, stalagmite, time series analys

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HCG35-P02

Room:Convention Hall

Time:May 27 18:15-19:30

Formation condition of deposits of sediment wave in the Neogene Aoshima Formation,
Kyushu Island, southwest Japan
ISHIHARA, Yoshiro1∗ ; ONISHI, Yuri1 ; KAWAKAMI-TAKII, Kiwako1
1

Department of Earth System Science, Fukuoka University

The Neogene Aoshima Formation, the uppermost part of a forearc basin fill of the Miyazaki Group, is well exposed along
the Nichinan Coast, in Miyazaki City, Miyazaki Prefecture. Sediment gravity flow deposits dominate this formation, showing
anomalous depositional sequences and thickness frequency distributions. The sediment gravity flow deposits are well correlated
along the palaeocurrent directions of the formation. These deposits, 10 cm to 30 cm thick, are traceable for about 10 km along
outcrops exposed at the coast. Sedimentary facies and statistical analyses of the bed thicknesses suggest an offshore depositionalsetting of a fan delta.
In the formation distributed along the Shirahama Coast of Miyazaki City, bed-by-bed correlations of the sediment gravity flow
deposits along approximately 700 m have been performed in our previous studies. In those results, the depositional topography
with a wavelength of approximately 600 m to 700 m suggested a sequence of sediment waves. In the present study, we calculated flow velocities of the sediment gravity flows forming the sediment waves and compare the consistency with sedimentary
structures in the sediment gravity flow deposits forming the waves.
The sediment wave deposits in the Aoshima Formation have the following characteristics. (1) The beds of the sediment gravity
flow deposit are composed of fine- to medium-grained sandstone. Lateral thickness fluctuations are dominant in the upper part of
the analysed section. (2) Waves showing wavelengths of approximately 600 m to 700 m have short stoss sides and long lee sides.
(3) The intervals of beds in the stoss sides frequently contain many rip-up clasts. (4) The dominant sedimentary structures in thesediment gravity flow deposits forming the waves exhibit spaced planner laminations and massive units. These characteristics
suggest that the deposits forming the sediment waves were deposited in an upper flow regime stage and that hydraulic jumps
occurred in the intervals of the stoss sides.
The flow velocities of the sediment waves were calculated by examining the relationship between the wavelength and flow
velocity of the sediment wave in previous studies. In the calculation, the density difference in the ambient fluid and sedimentgravity flow was 10 kg/m3 to 300 kg/m3 ; deposition-dominated flows that were not included in auto-suspension were considered.
The results indicate flow velocities of 3.0 to 17.3 m/s with a palaeoslope of 0.1 degree, 3.0 to 13.0 m/s in 1 degree, 3.0 to 6.5 m/s
in 2 degree, and 3.0-4.3 m/s in 5 degree. These estimated flow velocities correspond to the sedimentary structures in the upper
flow regime stage in the sediment gravity flow deposits forming the sediment waves.
Keywords: sediment wave, traction carpet, sediment gravity flow deposit, bed-by-bed correlation, flow velocity

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HCG35-P03

Room:Convention Hall

Time:May 27 18:15-19:30

Facies analysis of turbidite succession using borehole log data
ONISHI, Yuri1∗ ; SASAKI, Hana1 ; ISHIHARA, Yoshiro2 ; TAKANO, Osamu3
1

Graduate School of Science, Fukuoka University, 2 Department of Earth System Science, Fukuoka University, 3 Japan Petroleum
Exploration, JAPEX Research Center
Gamma-ray logging is regarded as the most sensitive method to lithofacies changes in boreholes. For this reason, identificationsof lithofacies in turbidite successions along a well-log succession are made mainly based on gamma-ray logs. Gamma-ray logs
are also analyzed using software, e.g, CycloLogT M for spectral analysis of gamma-ray logs, to detect sedimentary facies andstratigraphic variations, because the resolutions of the log data are limited for certain data intervals and the identifications arenecessary for objective interpretations. Such tools can be used to easily and objectively detect sandy or muddy horizons, estimate
scales of stratigraphic variations, and discover correlations in the log data. In this study, in particular, sedimentary facies wasanalyzed using the lamina identifying method proposed by Sasaki et al.(in press) and the Hurst analysis procedure using gammaray log data from turbidite successions.
The method of Sasaki et al. can provide reproducible and objective lamina boundary identifications by use of a combinationof change rates with median values from the gray-value profiles of digital lamina images. Because the method can identify
bicolored laminae, it was used for identifying intervals of sandstone-dominated and mudstone-dominated horizons in the logs.
The Hurst analysis can reveal the fractal nature of log data, and these data can be used to further characterize each unit of thehorizons identified by the method of Sasaki et al.
In the results, high and low-density sandy intervals and high and low-density muddy intervals were identified using the above
methods on the density logs (e.g., RHOB) from the gamma-ray log data. The Hurst analysis evaluated persistence, and the results
suggest that fluctuations in ”real” alternations affected the log-patterns of the intervals. It is suggested that corroboration of theresults from these methods can provide a new kind of robust sedimentary-facies analysis for turbidite succession.

Keywords: sedimentary facies analysis, turbidite succession, Hurst analysis, gamma-ray log

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HCG35-P04

Room:Convention Hall

Time:May 27 18:15-19:30

Three-dimensional models of alluvial plain considering sedimentary facies: an exampleof Kumamoto Plain
NAKAO, Kento1∗ ; ISHIHARA, Yoshiro1 ; NARUSE, Hajime1
1

Department of Earth System Science Faculty of Science, Fukuoka University, 2 Department of Geology and Mineralogy, Graduate School of Science, Kyoto University
Most alluvial plains in Japan are located in oceanfront areas, which are areas of high population density. Recent studies ofalluvial plains have focused on the construction of three-dimensional geological models and geotechnical maps in these areas
because such regions include geotechnically soft ground. Eto et al. (2008) constructed three-dimensional geological and geotechnical models of incised-valley fills beneath the Tokyo Lowland by using a method that requires neither an expert interpretation
nor specialist knowledge. Although evaluation of lithologic continuities should be included in the construction of such models,
this factor has not been considered in previous studies. Continuities of lithology are strongly affected by the sedimentary processes represented in the sedimentary facies. Therefore, three-dimensional models considering sedimentary facies will lead to
improvements in model accuracy.
The Kumamoto Plain distributed in the Kumamoto Prefecture, Kyushu Island, is located in a downstream area of the Shirakawa and Midori-kawa rivers originating from the Aso Caldera. Alluvial deposits in this area include the Shimabarakaiwan
Formation and the Ariake Clay Formation in ascending order. Lithofacies of the Holocene Ariake Clay Formation include
channel-fills and flood plain deposits of an inland bay area and coastal delta deposits in Shimabara bay (Hase and Iwauchi,
1996). In this study, we characterized the lithological distributions of the alluvial deposits by analyzing borehole data in the Kumamoto Plain, and we applied an improved construction method of a three-dimensional geological model to the alluvial deposits.
As a result, the Ariake Clay Formation well continuing from the bay to the inland areas is clearly visualized.

Keywords: alluvial plains, borehole database, continuities of lithology, The Kumamoto Plain, sedimentary facies, three-dimensional
geological model

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HCG35-P05

Room:Convention Hall

Time:May 27 18:15-19:30

Subsurface structure around Oumi basin
KITADA, Naoko1∗ ; ITO, Hiroko1 ; INOUE, Naoto1 ; MITAMURA, Muneki2 ; TAKEMURA, Keiji3
1

Geo-Resarch Institute, 2 Osaka City Univ., 3 Kyoto Univ.

Omi Basin is located in the central part of Shiga Prefecture which includes the largest lake in Japan called Lake Biwa. So as toclarify both geotechnical and geological properties in this area, Kansai Geo-informatics Network (KG-NET) has collected about
14,600 borehole data to add the exiting ”Kansai Geo-informatics Database”(GI-base). In this study, the sedimentary facies of theshallow subsurface strata have been introduced by using GI-base and some standard borehole data.
Because the topographical and geological characteristics of the basin obviously change for each local area, the sedimentary
facies are also complicate and difficult to be generally evaluated. So the discussion has been focused about mainly the eastern
and western part of Lake Biwa.
The eastern part of Lake Biwa has the largest plain in the Basin. The freshwater clays distribute continuously under the deltaic
deposit in the southeast, while the beach ridge and its back marsh are formed along the northeast lakeside. The soil properties of
the reclaimed lagoons and back marsh are specially soft and weak clays.

Keywords: alluvium, borehole, database, sedimentary environment

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HCG35-P06

Room:Convention Hall

Time:May 27 18:15-19:30

Chemical composition and classification of frutexites in Alwa Formation, Oman mountains, northern Oman
HONJO, Ren1∗ ; YOSHIDA, Kohki2
1

Graduate school of science and technology, Shinshu University, 2 Department of Geology, Faculty of Science, Shinshu University
The frutexites, showing irregular shrub structure, which was described as a micorostromatolites induced by microbial activity
by Maslov (1960). The structure with microlayering is interpreted to be formed by microbiotic activity with deposition of Fe
and Mn minerals (Jakubowicz et al., 2014). The frutexites were reported from the Lower Triassic Alwa Formation, which is distributed in the southeastern part of the Oman Mountains (Woods and Baud, 2009). This formation consist mainly of red colored
carbonate including peloidal wakestones and perodial packstones. The frutexites is occurred from the remarkable black colored
carbonate, which is called as sheet crack by Woods and Baud (2009) and is filled by submarine cement in the Alwa Formation.
This black colored carbonate encrusts the wall-rock surface of sheet crack. In this study, we aim to describe the microstructure
and chemical composition of this frutexites on the basis of microscopic observation and chemical analysis using EDS.
The predominant feature of the frutexites in the Alwa Formation exhibits 0.1-1.5mm long shrub structure consisting of microlayering by Fe-Mn rich carbonate minerals. Under microscope, two distinct layers showing orange and white colors arerecognized and the latter is developed in outer marginal layer of the shrub structure of these carbonate microlayers. In addition,
the black color shrubs, which are 0.1-0.5mm long and lack to orange colored layers, are also observed in the black carbonate.
The EDS analysis, using JSM-6510A in Shinshu University, shows the compositional difference of the micro layers of these
frutexites. The orange and white colored microlayers of frutexites contain Mg, Fe, Mn as a carbonate component, whereas Al
and P concentrates in the black colored microlayers. Thus, the frutexites in the Alwa Formation is classified by two types; MgFe-Mn rich and Al-P rich types. The shrub structure grew as a result of mineralization by microbial activity under fluctuating
conditions (Jakubowicz et al., 2014). Thus, this compositional differences and variety of frutexites is possibly related to themicrobial activity and bottom water condition during their growth stage.

Keywords: Triassic, limestone, chemical composition, Oman

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HCG35-P07

Room:Convention Hall

Time:May 27 18:15-19:30

Special differences of regressive systems during MIS 5e-4 in the Pleistocene Kioroshi and
Joso Formations, Shimosa GroupAKIYAMA, Daichi1∗ ; NAKAZATO, Hiroomi2 ; OKAZAKI, Hiroko3
1

Graduate School of Frontier Science, The University of Tokyo, 2 National Institute for Rural Engineering, 3 Division of Earth
Science, Natural History and Institute, Chiba
Paleo-Tokyo Bay, which the Middle to Upper Pleistocene Shimosa Group was deposited in, repeated appearance and disappearance under the condition of glacio-eustatic sea-level change, Kanto plain. The upper part of the Shimousa Group consistsof Kioroshi and Joso Formations, which were deposited during marine oxygen-isotope stage (MIS) 6 to 4. This study analyzed
sedimentary facies of the typical regressive systems developed at the inner part of bay and the open sea side, in Kioroshi and
Joso Formations, which is distributed the Joso Upland , in southern Ibaraki and northern Chiba Prefectures. As the result, lower
shoreface, upper shoreface, tidal inlet, beach, and marsh facies are recognized in the Kioroshi Formations. River and marsh
facies are recognized in the Joso Formation. Although similar sedimentary facies are recognized, the inner part of bay and theopen sea side have differences in their facies and grain size distributions. Fluvial facies of the inner part of bay consists of mud
to pebble, very poorly sorted. Large-scale trough cross-stratification is the predominant sedimentary structure. It shows typicalriver facies. On the other hand, facies of the open sea side consists of mainly medium-grained to coarse-grained sand, well sorted
comparison with the facies of the inner part of bay, and the constituent parts of mud is several percent. Trough cross-stratificationshows small-scale, and the iron sands is concentrated into laminae. Such as differences of facies reflect special differences the
paleogeography, during the regression. However, the cronocorrelation is needed to reconstruct about the paleogeography.
Keywords: regressive systems, Middle to Upper Pleistocene, Paleo-Tokyo Bay

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