MIS30-01

Room:304

Time:May 26 09:00-09:15

Biostratigraphy and carbon isotope stratigraphy of the Olenekian-Anisian pelagic deepsea section from Ogama, Ashio Belt
MUTO, Shun1∗ ; TAKAHASHI, Satoshi1 ; YAMAKITA, Satoshi2 ; SUZUKI, Noritoshi3 ; AITA, Yoshiaki4 ;SAITO, Megumi5 ; SUZUKI, Nozomi5 ; KUBOTA, Yoshimi51Department of Earth and Planetary Science, The University of Tokyo, 2 Department of Earth Sciences, University of Miyazaki,
Institute of Geology and Paleontology, Tohoku University, 4 Geology Lab, Faculty of Agriculture, Utsunomiya University,
5
Department of Geology and Paleontology, National Museum of Nature and Science3

The recovery of life after the end-Permian mass extinction occurred around Anisian (early Middle Triassic). At the OlenekianAnisian (Lower-Middle Triassic) boundary (O-AB), the lithologic change from claystone dominant facies to radiolarian-richbedded chert facies has been reported from the Panthalassic pelagic deep-sea sediments in Japan. This trend has been interpreted
to reflect a biotic recovery of the pelagic Panthalassa (Isozaki, 1997, Takahashi et al., 2009). However, spatial variations in thelithofacies of these pelagic deep-sea sediments have seldom been investigated in detail, due to the scarcity of well-preserved
sections. This study reports a high-resolution microfossil- and carbon isotope-based stratigraphy around the O-AB from a new
pelagic deep-sea section (Ogama section) situated in the Tochigi Prefecture, eastern Japan. The lower 8.5 m of the Ogama section
is composed of alternating claystone and chert, while the upper 9 m is composed of bedded chert. Age diagnostic fossils showthat the alternating claystone and chert interval can be correlated to the Spathian (upper Olenekian: uppermost Lower Triassic) tomiddle Anisian (lower Middle Triassic), and the bedded chert interval to the middle (to upper) Anisian. Organic carbon isotope
values show a positive peak near the lowest occurrence of the conodont Ch. timorensis. This fact accords with the carbonate
carbon isotope record reported from shallow-water marine carbonate sections.
The lithological transition from alternating claystone and chert to bedded chert facies near the OA-B has also been reported
from the well-studied sections in the Inuyama area, Central Japan (compiled in Ikeda et al., 2010). Although the timing of thislithologic transition is roughly coincident for the two study areas, a conspicuous difference in lithology is observed around the
O-AB. In the Ogama section, the O-AB falls within a 4 m thick, organic-rich black claystone dominant interval. In contrast,
the O-AB interval in the Inuyama area is composed mainly of grey siliceous claystone. This suggests that production and/or
preservation of organic matter was greater at the depositional grounds of the Ogama section. Further comparison of lithologic
characters of the two study areas could promote the understanding of the pelagic oceanic environments around the O-AB.
Keywords: Olenekian-Anisian boundary, Conodont, Radiolarian, Carbon isotope

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MIS30-02

Room:304

Time:May 26 09:15-09:30

Non-sulphidic anoxic conditions in the end-Early Triassic deep sea
TAKAHASHI, Satoshi1∗ ; YAMASAKI, Shin-ichi2 ; OGAWA, Kazuhiro3 ; KAIHO, Kunio3 ;TSUCHIYA, Noriyoshi2
1

Department of Earth and Planetary Science, University of Tokyo, 2 Graduate School of Environmental Studies, Tohoku University,, 3 Graduate School of Science, Tohoku University
This study focuses on an upper Lower Triassic (Spathian) to lowermost Middle Triassic (Anisian) section representing thecentral Panthalassic deep sea. Analysed organic carbon isotope ratio (δ 13 Corg ) records from the section demonstrate that lower
values in the Spathian increase by up to 6 ‰ at the Spathian ‒ Anisian transition. This trend accords with the carbonate carbon isotope (δ 13 Ccarb ) record from shallow water carbonate sections. The end of the Early Triassic trough of δ 13 Corg consistsof black chert deposits sandwiched by black claystone beds in the study section. In these black-coloured beds and underlying
siliceous claystone beds, higher concentrations of redox-sensitive elements, such as Mo and V, and coinciding low sulphidesulphur isotope ratios (δ 34 Ssulphide ) and previously reported sulphur-bearing organic compounds are present, suggesting anoxic
deep water. As enrichment factors of Mo are not higher than the typical sulphidic trend, these anoxic conditions did not become
sulphidic. Oxygen-poor conditions coinciding with a carbon isotope trough have been also reported in late Early Triassic strata
from shallow-water sections. These coincidences imply global environmental perturbations related to the delayed recovery oflife after the end-Permian mass extinction.
Keywords: pelagic deep-sea, oceanic anoxia, trace element, Triassic, carbon isotope

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MIS30-03

Room:304

Time:May 26 09:30-09:45

Stratigraphy and age of stratiform manganese deposits in the Chichibu Belt, JapanTOMIMATSU, Yuki1∗ ; ONOUE, Tetsuji1
1

Earth and Environmental Sciences, Graduate School of Science and Technology, Kumamoto University

The chert-hosted manganese deposits have been known to occur in the Triassic to Jurassic chert or chert-greenstone complex
within a Jurassic accretionary complex, Chichibu Belt, southwest Japan. In order to reveal the specific age of the manganesedeposits, this study investigated the occurrence and depositional age of the seven localities of manganese deposits (Taura, Tinu,
Takahama, Kubodomari, Takahira, Kakinoo, Akimoto) in Saiki and Takachiho areas in the Chichibu Belt of eastern Kyushu.We
also performed XRF analyses to infer the origin of manganese deposits.
Triassic and Jurassic radiolarian fossils were obtained from the 6 samples of the chert bed below the manganese deposits in thethree localities (Takahama, Takahira, Akimoto). In Takahira locality, the manganese deposit occurs above the massive chert withakashiro silicastone. The red bedded chert above the manganese deposit yields radiolarian fossils such as; Trialatus longicornutus
and Poulpus carcharus . These radiolarians show that age of manganese deposits can be correlated with the late Carnian age. In
Takahama and Akimoto localities, the bedded chert above the manganese deposit is gray and occurs the Lower Jurassic radiolarianfossils (e.g., Trillus elkhornensis and Tricolocapsa plicarum ). The XRF analysis revealed that the geochemical features of themanganese deposits in the study area is geochemically similar to the modern submarine hydrothermal manganese deposits.
Consequently, manganese deposits in the eastern Kyushu were deposited by hydrothermal activity in an open-ocean setting
around the late Carnian and Early Jurassic. The large volumes of flood basalts were erupted in the Carnian and Early Jurassic,
and their ages are consistent with the depositional ages of the manganese deposits from the Chichibu Belt in eastern Kyushu.

Keywords: Chichibu Belt, stratiform manganese deposits, radiolarian biostratigraphy, Upper Triassic, Lower Jurassic, volcanic
activity

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MIS30-04

Room:304

Time:May 26 09:45-10:00

Chemostratigraphy of the Middle Triassic bedded chert sequence in the Mino Belt, central
Japan
SODA, Katsuhito1∗ ; ONOUE, Tetsuji1
1

Kumamoto Univ.

Previous studies have proposed that the alterations of chert and shale beds in the bedded chert sequence of the Japanese Jurassic
accretionary complex are paced by precession and eccentricity cycles, especially chert bed thickness variation is interpreted as
productivity fluctuations. However, the cyclostratigraphic interpretations and the continuity of sequence between sections await
further verification (Ogg, 2014). In this study, we focus on shale beds as geochemical proxies for stratigraphic correlation andpaleoclimatological interpretation. Then we conducted geologic survey at Section M, CH2L, L, and B (Anisian and Ladinianbased on detailed radiolarian biostratigraphy by Sugiyama, 1997), reconstructed the composite column using stratigraphic correlation of lithological associations between sections, and collected shale bed samples with bed by bed resolution for geochemical
analysis (more than 500 samples). The reconstructed lithostratigraphy of the Middle Triassic bedded chert sequence consists oflower gray bedded chert, lower red bedded chert, upper gray bedded chert, and upper red bedded chert in ascending order (Ikeda
et al., 2010). The elemental compositions in shale beds are determined by XRF analysis. In presentation, we will discuss about
the geochemical characteristics of shale beds, the chemostratigraphy of the Middle Triassic bedded chert sequence, and theirimplications.

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MIS30-05

Room:304

Time:May 26 10:00-10:15

Carbon isotope record from the Upper Triassic bedded chert in the Mino Belt, central
Japan
ONOUE, Tetsuji1∗ ; IKEHARA, Minoru2 ; SODA, Katsuhito1 ; YAMASHITA, Daisuke1
1

Kumamoto University, 2 Center for Advanced Marine Core Research, Kochi University

The Late Triassic was characterized by several marine and terrestrial biotic turnover events prior to the end-Triassic mass
extinction. The causes of the end-Triassic mass extinction and these Norian to Rhaetian biotic turnover events are still the subjectof debate. In order to infer the Norian to Rhaetian (Late Triassic) environmental changes in a pelagic realm of the Panthalassa
Ocean, the stratigraphic variations of TOC and δ13Corg of the bedded chert succession in the Sakahogi section were examined.
The Sakahogi section (˜26 m in thickness) crops out in the Mino Belt, central Japan, and consists of the red to greenish-graybedded chert. The radiolarian biostratigraphy indicates a middle Norian to Rhaetian age of the bedded chert. The bedded chertof the Sakahogi section is reconstructed as a deep-sea sediment of pelagic facies forms in an open ocean realm of the Panthalassa
Ocean. Our analysis shows that the middle Norian samples record stable vaues until the late middle Norian. This stability is
disturbed by a small negative δ13Corg excursion at the middle Norian ejecta layer (Sakahogi ejecta). TOC values increase acrossthe middle and upper Norian boundary interval. This interval is marked by a minor increase in δ13Corg value (˜1 ‰).
Keywords: Triassic, bedded chert, carbon isotope

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MIS30-06

Room:304

Time:May 26 10:15-10:30

Deep-ocean acidification and volcanism across the Triassic-Jurassic extinction event
IKEDA, Masayuki1 ; HORI, S., Rie2∗ ; NAKADA, Ryoichi3 ; OKADA, Yuki2
1

Shizuoka Univerisity, 2 Ehime University, 3 Tokyo Institute of Technology

Triassic-Jurassic (T-J) extinction event marks one of the Big Five mass extinction events of the Phanerozoic. The emerging
consensus points to volcanic activity at the Central Atlantic Magmatic Province (CAMP) as the ultimate cause of the extinction,
yet the underlying nature of global environmental changes that accompanied the biotic turnover remain elusive. We present
chemical and mineralogical studies across the T-J transition of the deep-sea chert sequence (Inuyama, Japan). Depleted hematite
content normalized by terrigenous material occurred just before the T-J extinction with significant change in color from brickred to purple. This suggests the loss of authigenic hematite due to the deep-ocean acidification, which is consistent with therock magnetic records of Abrajevitch et al. (2013). This timing is consistent with the CAMP volcanism, implying a catastrophic
release of greenhouse gases as causes of deep-ocean acidification. Across the T-J transition, MgO/Al2O3, Fe2O3/Al2O3, andAl2O3/SiO2 increased with change in color from brick red to dusty red. These geochemical trends are consistent with those of
weathered CAMP basalts in arid area (Dal Corso et al., 2014), implying that weathered CAMP basalts became the considerable
source of aeolian dust in pelagic Panthalassa after the T-J extinction event.
Keywords: Triassic/Jurassic, acidification, volcanism, extinction

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MIS30-07

Room:304

Time:May 26 10:30-10:45

Carbon and oxygen isotopes record of Upper Triassic limestone in the Kardolina section,
Slovakia
SHIROZU, Hideko1∗ ; MICHALIK, Josef2 ; KUSAKA, Soichiro3 ; YAMASHITA, Misa4 ; YAMASHITA, Katsuyuki4 ;ONOUE, Tetsuji1
1

Graduate School of Science and Technology, Kumamoto University, 2 Slovak Academy of Sciences, 3 Research Institute for
Humanity and Nature, 4 Graduate School of Natural Science and Technology, Okayama University
Triassic / Jurassic (T/J) boundary of approximately 201.3 million years ago is known as a stratigraphic boundary recorded
one of the big five Phanerozoic mass extinctions. Catastrophic processes such as widespread eruption of the Central Atlantic
Magmatic Province (CAMP) flood basalts and extraterrestrial impacts have been proposed to account for the mass extinction
event. This paper reports the results of carbon and oxygen isotopes analysis from the uppermost Triassic limestone in the
Kardolina section, Slovakia. The Kardolina section is crops out on a steep western slope of the Mt Palenica in the Belianske
Tatry Mts as the most continuous section from the uppermost Triassic (Rhaetian) Fatra Formation. The Fatra Formation isshallow marine carbonate sequence and is overlain with a sharp contact by marine shale of the lowermost Jurassic (Hettangian)Kopieniec Formation. The Rhaetian age of the Fatra Formation was determined by foraminifera fossils. Several excursions ofcarbon and oxygen isotopes exist in the Fatra Formation. The large negative carbon isotope excursions (CIE) were found in atleast four stratigraphic levels. Although the Fatra Formation is composed of packstone and grainstone, the CIE occurred during
the deposition of non-fossiliferous lime-mudstone or ostracod lime-mudstone. The largest negative CIE occurs just before theT/J boundary. The cause of this negative CIE at the vicinity of T/J boundary remains uncertain. However it is assumed that the
Kardolina section was exposed on the ground by sea-level fall, and subjected to diagenesis of terrestrial water. The large CIE
may possibly be associated with sea-level change of the Kardolina section.
Keywords: carbon and oxygen isotopes, limestone, Triassic/Jurassic boundary, Rhaetian, carbon isotope excursion, sea-levelchange1/1

MIS30-08

Room:304

Time:May 26 11:00-11:15

Reconstruction of mid-Cretaceous oceanic plate stratigraphy in the Hidaka-cho area, Southcentral Hokkaido
SAITO, Asami1∗
1

Graduate School of Science and Technology,Niigata University

Jurassic to Early Cretaceous accretionary complexes were formed by subduction of an old and cold oceanic plate more than
100 m.y. old. Whereas those in the Late Cretaceous and Paleogene periods formed upon a young and warm oceanic plate, whichspent less than 30 m.y. from its birth to subduction. The character of the boundary between the oceanic crusts of differing ages isleft unknown. Terrigeneous mudstones of the Ganpiyama Comlex (Kawamura et al., 2001) in the Kamuikotan Zone of Hokkaido
Yields radiolarian fossils of late Albian to early Cenomanian (Agency for Natural Resources and Energy, 1989). This study aims
to clarify the mode of connection between the old and new oceanic plates reconstructing oceanic plate stratigraphy in the Ganpiyama Complex, which might have formed in the turning point from the old to young plate subduction. This presentation willshow reconstructed oceanic plate stratigraphy based on observation of fragmented sedimentary successhion and newly obtained
radiolarian ages.
The Ganpiyama Complex occurs surrounded by serpentinite and underwent very low grade high-pressure metamorphism withoccurenses of alkali pyroxene and aragonite (Kawamura et al., 2001). This complex consists mainly of terrigenous clastic rocks
such as black mudstone and broken turbidites, with lesser amounts of oceanic rocks such as metabasalt and chert. Fragmental
sedimentary successions e.g. from metabasalt to chert, and chert via alternation of chert and siliceous mudstone to terrigenous
clastic rocks are observed in many sections. These allows us to complement the original full sequence of metabasalt, red mudstone (<1 m thick), bedded chert (5-10 m) with limestone intercalations, alternating beds of chert and siliceous mudstone (1-1.5m), and terrigenous mudstone and sandstone (>15m) in stratigraphically ascending order. Metabasalts underlying bedded chert
comprise volcanic breccia associated with clasts and matrices of chert. Also found are isolated bodies of pillow and massive
lava, which do not accompany with chert. In addition, there is variation in sediments overlying the metabasalt there are cases inwhich one of red mudstone, red chert or alternating beds of chert and siliceous mudstone covered metabasalts. Volcanic brecciawith chert clasts suggest existence of high reliefs on the ocean floor and mass wasting on their slopes. Diversity of sediments
overlying the breccia may also have reflected rough topography. Radiolarian fossils were newly obtained from pelagic chert andhemipelagic alternation of siliceous mudstone and chert. In spite of extensive recrystallization, early Aptian or earlier Cretaceous
fauna from chert, and late Aptian to early Albian fauna from alternation of chert and siliceous mudstone were identified. The
oldest limit of the chert sedimentation has not been determined well. However, it feels not so old as Jurassic taking into accountthe small thickness is of the chert (5-10m). The age of the subducted oceanic plate in the mid-Cretaceous is estimated as 3040m.y, as the age difference of pelagic sediments and terrigenous clastic rocks. The old oceanic plate is thus considered to havebeen altered by the young one until the time of formation of the Ganpiyama Complex. Early Cretaceous accretionary complexes(Iwashimizu Complex of the Kamuikotan Zone and the Naizawa Complex of the Idonnappu Zone) both formed in ˜130Ma contain Triassic chert and limestone as suggestive of the old plate subduction. Therefore, it is considered that the boundary between
the two plates passed Hokkaido during 130-100Ma.

Keywords: oceanic plate stratigraphy, accretionary complex, radiolaria

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MIS30-09

Room:304

Time:May 26 11:15-11:30

Jurassic intraoceanic arc offshore Japan
UEDA, Hayato1∗
1

Niigata Univ.

The Sorachi-Yezo Belt in central Hokkaido is based on ophiolitic rocks represented by the lower Sorachi Group including the
Horokanai Ophiolite. Controversy of their origins is responsible for many unsolved problems such as reconstruction of oceanic
plates and correlation to SW Japan. This paper tests a marginal basin model with a Jurassic intraoceanic arc, introducing petrology of the Gunkanyama Ophiolite complex in the Mitsuishi area, southern Sorachi-Yezo Belt.
The Mitsuishi area has been known as a locality of serpentinite melange with high-pressure (HP) metamorphic blocks representative of the Kamuikotan Zone. This study has revealed that the pre-Neogene rocks of this area comprise a three parallelzones of low-grade HP metamorphic accretionary complex, the Gunkanyama Ophiolite, and serpentinites melange. These rocks
are unconformably overlain by Neogene deposits, and folded together. The Gunkanyama Ophiolite is regarded as an amalgamateof fault-bounded slices of plutonic-hypabyssal complex, ultramafic cumulate, and partly serpentinized harzburgite. No effusive
and sedimentary rocks are found.
The plutonic-hypabyssal complex consists mainly of mafic cumulates and dikes, associated with minor dikes and small bodies
of diorite and tonalite. 160-165 Ma (late Middle Jurassic to early Late Jurassic) zircon U-Pb ages have been obtained from these
felsic rocks. Igneous rocks are dominated by basaltic andesite poor in HFS elements, suggestive of volcanic arc. Some of them
are classified as boninites in composition. Taking into account the absence of continental basement rocks, the ophiolite probably
originated from immature intraoceanic arc. It might have existed ocean-ward from the trench which produced the Jurassic accretionary complex in Japan, and lay upon a distinct plate from the Triassic or older oceanic plate responsible for Jurassic and Early
Cretaceous accretionary complexes and the Kamuikotan blueschist metamorphism.
The lower Sorachi Group (& Horokanai Ophiolite) shows no trace of island arc activity in the Jurassic period, with basalts with
MORB or OPB chemical affinity. Genetic relationship between the Gunkanyama and Sorachi ophiolites are thus left unknown.
However, it is not difficult to speculate that these coeval ophiolites with similar geotectonic positions together belonged to asingle plate. This leads to a hypothesis that they comprised an arc - backarc system.

Keywords: oceanic plate paleogeography, Jurassic, ophiolite, inraoceanic arc

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MIS30-10

Room:304

Time:May 26 11:30-11:45

What does the radiolarian Spumellaria/Nassellaria ratio indicate?
MATSUOKA, Atsushi1∗
1

Niigata University

Spumellaria and Nassellaria are major orders in radiolarians. The Spumellaria/Nassellaria ratio has been used in monitoring
environmental changes in the past oceans. However, what the ratio indicates is not well understood. It is noteworthy to pointout that the ratio is strongly affected by taphonomic processes and careful application is needed. Detailed observations of avariety in feeding behavior of cultured radiolarian specimens make it possible to understand the relationship between skeletal
morphology and feeding behavior. Multi-segmented nassellarians require much larger prey than any other radiolarians. The ratioof multi-segmented nassellarians to total radiolarians is regarded as another proxy in monitoring ecosystem in the pelagic realm.
Keywords: radiolaria, Nassellaria, Spumellaria, paleoenvironment, proxy, pelagic realm

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MIS30-11

Room:304

Time:May 26 11:45-12:00

Trace fossils of Ordovician chert and siliceous rocks from Newfoundland, northeastern
CanadaKAKUWA, Yoshitaka1∗1

Gas Hydrate Research Lab., Meiji Univ.

Sudden and continuous increase in biodiversity in Ordovician is named as ”Great Ordovician Biodiversification Event” (Webby,
2004). But the evolution of benthic animals in pelagic realm remained unstudied. One of the typical sediment of the pelagic
ocean bottom is radiolarian chert, and the studies on the chert and the associated siliceous rocks especially on trace fossils
recorded in those rocks are essential. Records of trace fossils in the upper Cambrian to the upper Ordovician chert and siliceous
rocks are examined in detail that is summarized as follows; tiny and simple ones in the Late Cambrian increase their size andmorphological varieties in the late Middle Ordovician (Kakuwa & Webb, 2007; 2010), and the result is supported by Percival(2012). This presentation reports the Canadian case.
Chert and siliceous sediments had been deposited by the spreading and deepening of Iapetus Ocean, and the rocks are exposedin the Newfoudland, northeastern Canada. Examined are three rock units; (1) Shoal Arm Formation, which is composed of red
chert, gray chert and black shale in ascending order, conformably overlies the volcanic rocks of the Wild Bight Group, and isconformably overlain by turbidite sandstone of the Gull Island Formation, Badger Group. The age of the chert of Shoal Arm
Formation is almost correlated to the N. gracilis zone that is correlated to early half of Sandbian (Caradocian). (2) Strong Island
Chert, which is composed of argillaceous chert and siliceous mudstone with some turbidite sandstone interbeds, overlies tholeiitic and alkaline pillow lava and pillow breccia of the Lawrence Head Formation. The age is correlated to the basal Darriwilian
to lower Sandbian. (3) Sanders Cove Formation, which is composed of red and green siliceous mudstone, chert (silicified tuff?)and volcaniclastic sandstone turbidite overlies volcanic rocks of the Tea Arm Formation. The age is Tremadocian to Dapingian.
All the geologic information is based on O’Brien (2012).
These three units of Ordovician siliceous rocks are not comparable to the typical pelagic sediment of the deep-sea ocean, but
the general evolutionary trend of the trace fossils is consistent with the Australian case. The lower Ordovician siliceous rocks of
the Sanders Cove Formation bears only small and tiny burrow tunnels of Planolites-type. And small and simple burrow tunnelsof Planolites-type both in the lower section of the Shoal Arm Formation and the Strong Island Chert change to large burrows
such as Teichichnus-type in the upper section.
This general evolutionary trend is overlapped by the development of the basin and/or local changes in the environment. The
early stage of the formation of the basin allowed only small and simple type burrows even in an oxidized basin of the Late
Ordovician time. Frequent anoxic events in the later half, on the other hand, interrupted the oxygenated environment of large
Teichichnus-type burrows.
Keywords: trace fossil, Ordovician, chert, Canada, Teichichnus, evolution

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MIS30-12

Room:304

Time:May 26 12:00-12:20

Molluscs in pelagic realm: general characteristics in morphology and ecology
SASAKI, Takenori1∗
1

The University Museum, The University of Tokyo

Molluscs are the most thriving living animals in the ocean, and their fossil records are rich and continuous from the Cambrianto Holocene. The majority of molluscan groups are benthic, but part of them have adapted to a planktonic or pelagic life. Notable
examples include pteropods, heteropods, janthiniids and several genera of nudibranchs in gastropods. In cephalopods, many
species are pelagic or actively swim. These non-benthic molluscs segregate their habitats from the epipelagic to abyssopelagiczones, and a large number of species are known to migrate vertically. Their life habit is regulated by numerous environmental
factors such as light, nutrients, temperature and water pressure. A specialized mode of life often has severe constraints in morphological diversity: species in pelagic realm are characterized by a thin-shelled or shelless body, a limited spectrum of coloration,
sensitivity to illumination, and buoyancy control. These general characteristics are manifested particularly by comparison withthose of benthic species.
Keywords: pelagic realm, Mollusca

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MIS30-P01

Room:Convention Hall

Time:May 26 18:15-19:30

Establishment of pelagic deep-sea sedimentary sequence of lower Permian in the Tamba
belt, Southwest Japan
UCHIDA, Koya1∗ ; TAKAHASHI, Satoshi1 ; MUTO, Shun1 ; TASHIRO, Takayuki1 ; SUZUKI, Noritoshi2
1

Department of Earth and Planetary Science, the University of Tokyo, 2 Graduate school of science, Tohoku University

The Carboniferous and following early Permian are associated with climate changes related to tectonics and glaciations. The
development of ice-sheets occurred on the Gondowana continent, which was placed around the southern polar region. Repeatedincrease and decrease in the volume of such ice sheets have been suggested by the oxygen isotope ratio variations of carbonate
fossils (e.g., Chen et al., 2012). According to previous researches, the fluctuation of ice-sheet volume occurs in the time interval of
from one million years to several million years. Contemporaneous pelagic deep-sea sediments would provide materials available
for the reconstruction of environmental conditions such as oceanic ventilations and biotic productivity, but their records havebeen poorly known. The delay in the establishment of Carboniferous and lower Permian pelagic deep-sea stratigraphy is themain reason of this problem. The Paleozoic to Mesozoic deep-sea sedimentary rocks including the lower Permian are preservedin Japanese accretionary complexes. Among previous researches, Ishiga et al. (1982) reports one of the best lithologic sectionsof lower Permian deep-sea. This section is named the Funaeda section, and located in Yagi area, Northwest of Kyoto city. The
Funaeda section is composed of grey and red colored bedded chert. Although Ishiga et al. (1982) examined the age diagnostic
radiolarian fossils, the Permian biostratigraphy has recently been updated, and therefore more detailed discussion on the age
assignment of this section is required.
In this study, detailed field works on the Funaeda section were conducted, and the section was divided the Funaeda section into
five subsections, namely Fd-A˜E sections. We found conodont fossils from the uppermost and the middle part of the Fd-B section.
Some specimens are identified Mesogondolella sp.. Occurrences of these species are limited within the Cisuralian, suggestingthat the Fd-B section belongs to the Cisuralian. To observe each stratum in detail, we made polished rock specimens for the Fd-B
section. We found periodic variations in the thickness of bedded chert, rock color and lamina preservation. Thickness, rock color,and lamina preservation of the Fd-B section vary every ca.50, 4 and 48 beds, respectively. In this presentation, we will discussthese lithologic features and their relationship with the paleo-environmental conditions at the early Permian pelagic ocean.

Keywords: early Permian, pelagic deep-sea, bedded chert

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MIS30-P02

Room:Convention Hall

Time:May 26 18:15-19:30

Fault zone structure in pelagic sedimentary rocks: an example from the thrust fault in theJurassic accretionary complex
KINOSHITA, Takahiro1∗ ; UJIIE, Kohtaro1 ; TABATA, Hiroki1 ; SAITO, Tsubasa1 ; KOUKETSU, Yui2
1

University of Tsukuba, 2 The University of Tokyo

The Integrated Ocean Drilling Program (IODP) Expeditions 343 revealed that the plate-boundary faulting including the shallow
coseismic slip during the 2011 Tohoku-Oki earthquake was highly localized along the smectite-rich pelagic clay of less than 5 m
thick. This suggests a stratigraphic control on long-term evolution of plate-boundary faults and coseismic slip in shallow portionsof subduction zones. However, little is known about deep portions of subduction zones. Here, we examined how the fault zone
structure develops in pelagic sedimentary rocks based on detailed structural analysis of the thrust fault in the coherent chert-clastic
sequence of the Jurassic accretionary complex in central Japan. The studied thrust is thought to branch from the plate-boundary
fault, which separates the early Middle Triassic cherts and carbonaceous claystone above from the Middle Jurassic siliceous
mudstone below. The stratigraphy at the base of the hanging wall (i.e., carbonaceous claystone and black chert in the base,gray chert, and red chert in ascending order) represents the mid-Triassic recovery from the deep-sea anoxic event that occurred
across the Permo-Triassic boundary, with its total carbon content increasing from 0 to 8.5 wt% toward the base. The fault zoneis ˜20 m in thickness, and the footwall siliceous mudstone is widely damaged forming foliated cataclasite. In contrast, only
˜1 m-thick chert is fractured and brecciated in the hanging wall. In particular, the faulting is concentrated into the 5 cm-thickcataclasite defined by the fragments of black chert in the carbonaceous clay matrix. Notably, a few millimeters-thick dark layer
sharply cuts the cataclasite. On microscopic scale, this dark layer shows the appearance of fault and injection veins, roundedand embayed vein boundaries, and the presence of muscovite microlites in amorphous matrix, which are the characteristics ofpseudotachylytes. Our results indicate the faulting including seismic slip is highly localized along the carbonaceous claystone
and black chert. This suggests that a stratigraphic control on fault localization also occurred in deep portions of the subduction
zone, which appears to be related to deposition of carbonaceous material during deep-sea anoxia.
Keywords: pelagic sedimentary rocks, carbonaceous material, deep-sea anoxic event, pseudotachylyte, chert-clastic sequence

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MIS30-P03

Room:Convention Hall

Time:May 26 18:15-19:30

Geology and radioralian fossils of the Misogawa Complex of the eastern Mino Terrane in
the Kaida area, Nagano Prefecture
HAKOIWA, Hiroaki1∗ ; MATSUOKA, Atsushi11

Department of Geology, Niigata Univeristy

The Sawando, Shimashima and Misogawa Complexs are exposed in the eastern part of the Mino Terrane. The Sawando
and Misogawa Complexs are regarded to be formed by off-scraping accretion. On the other hand, the Shimashima Complex
distributed between the Sawando Complex and the Misogawa Complex is considered to be formed by different processes. In thisstudy, we intended to clarify whether the Shimashima Complex exists around the boundary between the Sawando Complex and
the Misogawa Complex in the Kaida area, Nagano Prefecture.
The study area is composed by the A, B and C formations. The A formation is dominated by siliceous rocks, forming an
imbricate structure. Cherts in the A formation yielded radiolarian fossils indicative of the Middle Norian to Early Rhaetian.
The B formation is dominated by sandstone and alternating beds of sandstone and mudstone. The C formation is dominated by
mudstone. These lithologic features are similar to those of the Misogawa Complex. No geological unit similar to the Shimashima
Complex in lithology has been found in the Kaida area.

Keywords: Sawando Complex, Shimashima Complex, Misogawa Complex, Late Triassic, radiolaria

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MIS30-P04

Room:Convention Hall

Time:May 26 18:15-19:30

Deformational environment of the Pleistocene Ashigara group along the northern marginof the Philippine sea plate
KOBAYASHI, Kenta1 ; KONAKAWA, Masato2∗
1

Dep. Geol., Fac. Sci., Niigata Univ., 2 Grad. Sch. Sci. & Tech., Niigata Univ.

On the northern convergence border of the Philippine Sea plate, Pleistocene Ashigara group (1.6-0.5Ma) filled a trough.
Miocene Tanzawa group is distributed on the north side, and both are bounded with the Kannawa fault system. The Kannawa
fault system is divided into five groups of active faults (e.g. Shiozawa fault system: NE-SW, sinistral-reverse). The Shiozawa
formation (conglomerates) which is the high-end strata of the Ashigara group is distributed over the southeastern side of the
Shiozawa fault. Parts of the conglomerates are deformed remarkably. P-R1 cataclasites are distributed over the range of 600m
from the Shiozawa fault. The shear sense is reverse fault mainl. Quartz grain becomes fine fragment by crush, and biotite does
basal slip, it is thought that this cataclasite was formed under environment of 250-300 oC, and 10km in depth. It is necessary toassume uplift rate more than 10m/Ka or an abnormally high geothermal gradient.
Keywords: Kanagawa Prefecture, Ashigara group, Shiozawa formation, cataclasite, coalification, Philippine sea plate

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MIS30-P05

Room:Convention Hall

Time:May 26 18:15-19:30

Reconsideration of the Tanakura shear zone north extension in the Oisawa tectonic zone,
Yamagata Prefecture
WAKABAYASHI, Akiho1∗ ; KOBAYASHI, Kenta1
1

Department of Geology, Faculty of Science, Niigata University

In recent studies, it is thought that the northern extension of the Tanakura tectonic line receives flexure or the modification of
the base in the Nagai Basin western margin fault zone and lies behind in the east of Asahi mountainous, after having gone along
the Ringo area, Yamagata Prefecture. On the other hand, possibility to extend the Tanakura shear zone formed with the activityof the Tanakura tectonic line in the Oisawa tectonic zone of the Asahi mountainous eastern margin is suggested in some studies.
Therefore I investigated the Oisawa area for the purpose of the elucidation of the geological structure history to reconsider the
Oisawa tectonic zone as northern extension of the Tanakura shear zone.
As a result of investigation, I elucidated that there are ten actual faults in this area and is able to estimate one fault. Also,
according to the geological map which I made in this investigation, in perspective this geological feature has the tendency of the
N-S direction and the fold axis develops in the NNE-SSW direction. The fold axis of NNW-SSE direction developing along thefault exist locally. In addition, the stratigraphy of the Oisawa area is different every block divided by faults, and the western blockand an eastern and southern difference divided by Sagaegawa fault are particularly clear. Once more, I elucidated a shear senseof each faults and elucidated that Sagaegawa fault and Oisawa fault were affected by dip-slip and strike-slip inversion tectonics.
From those results, the basin of the Oisawa area had a characteristic same as the Yamatsuri Basin of a strike-slip basin formedin the southern part of Tanakura tectonic line when Oisawa area examined the possibility that it was a strike-slip basin. Therefore
I judged Oisawa area to be more likely to be a strike-slip basin and made the tectonic development model of the Oisawa area
based on a shear sense of each faults. When strike-slip inversion tectonics influences a basin of the Oisawa area like the modelthat I made, it is limited in 15-12Ma in a timing of strike-slip inversion tectonics in the Oisawa area, and Oisawa tectonic zone ismore likely to be the north extension of the Tanakura shear zone.

Keywords: Oisawa tectonic zone, Tanakura shear zone, Tanakura tectonic line

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