BPT07-01

Japan Geoscience Union Meeting 2016

Reconstruction of Permian-Triassic ocean redox conditions based on laminae preservationand pyrite framboids from the pelagic Panthalassic Ocean
Akane Mizutani1, *Satoshi Takahashi1, Jun Ishida1, Shinji Yamamoto1, Masayuki Ikeda2, Kazumi Ozaki3,
Megumi Saitoh4, Nozomi Suzuki4, Ryuji Tada1
1.Department of Earth and Planetary Science, University of Tokyo, 2.Shizuoka University,
3.Atmosphere and Ocean Research Institute.University of Tokyo, 4.Division of Paleoenvironment andPaleoecology Department of Geology and Paleontology National Museam of Nature and Science
Widespread oceanic anoxia has been implicated as an important factor in the Permian -Triassic mass
extinction and the delayed recovery of Early Triassic marine ecosystems. This study investigatesthe composite columnar section of the deep-sea Permian-Triassic boundary section preserved in theaccretionary complex in Northeast Japan. This columnar section consists of the Upper Permian bedded
chert and siliceous claystone, and overlying the end-Permian to earliest Triassic black claystone.
The mass extinction horizon places in the base of the black claystone, and top of the reconstructed
black claystone corresponds to 226.7 kilo year after the extinction event based on sedimentation
rate estimated by Takahashi et al. (2014). The careful observation of polished cross sections
identified thinly laminated structures in the end-Permian to earliest Triassic claystone interval.
Our observation on the polished specimen revealed small and well sorted framboids (average
diameters are 4 μm and their standard deviations are 1.1 μm) suggesting that sulfidic water column
prevailed during the end Permian mass extinction and subsequent time interval corresponding to theoverlying 30 cm. Well preserved laminae occur within the same stratigraphic interval, suggesting
stagnant benthos activity due to anoxic bottom water condition under sulfidic water column. On theother hand, well preserved laminae appear again in the overlying earliest Triassic horizon, but
size of pyrite framboids are not so small (average diameters are more than 7μm), suggesting anoxic
but non-sulfidic water column condition. These facts indicate water column sulfidic episodes
sustained for less than 50 kilo years in the pelagic Panthalassa.
Keywords: Permian, Triassic, Mass extinction, Pelagic deep sea, Pyrite Framboids©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-01 -BPT07-02

Japan Geoscience Union Meeting 2016

Redox conditions of late Early Triassic oceanic region around the South Kitakami
Microcontinent*Kazuko Yoshizawa1, Satoshi Takahashi1, Masayuki Ehiro2, Takanobu Tsuihiji1, Shun Muto1, Takayuki
Tashiro1, Tsuyoshi Iizuka1, Masato Tanaka1, Yoshio Takahashi1
1.Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo,
2.The Tohoku University Museum, Tohoku University
After the end-Permian mass extinction (EPME), biotic recovery required more than 5 million years
during the Early Triassic. Evidence of recovery such as the emergence of complex ecosystems andhigh biodiversity appeared in the late Early Triassic to Middle Triassic (Chen and Benton, 2012).
The fossil evidence of a complex food chain was reported from shallow-marine strata of late
Olenekian (Spathian), late Early Triassic age, in the South Kitakami Microcontinent that was
located in the low-latitude Tethys-Panthalassa border (Ehiro, 2001). These strata belong to theOsawa Formation in the South Kitakami Belt, now distributed in Northeast Japan, and arecharacterized by well-preserved parallel laminae and the occurrence of the oldest ichthyosaurs(Shikama et al., 1978; Yamanaka and Yoshida, 2007). However, the depositional environment of thesestrata has been poorly understood. The present study aims to reveal detailed redox conditions in
the Spathian shallow marine region around the South Kitakami Microcontinent based on observation of
the sedimentary structure (laminae preservation), mode of occurrence of pyrite, and geochemical
proxies (redox-sensitive elements). Referring to the type columnar sections described by Kamata andTakizawa (1992), four lithologic sections corresponding to the lower, middle, and upper parts of
the Osawa Formation were identified. From these sections, 49 rock samples were collected for thinsections, polished specimens, and geochemical analyses (ICP-AES and ICP-MS). Observation ofpolished rock specimens indicates that laminae were well-preserved in mudstone from the middle partof the Osawa Formation whereas laminae were not visible in the lowermost and uppermost parts. These
trends indicate that the middle part of the Osawa Formation was deposited under conditions of lower
benthos activity than the lowermost and uppermost parts. Mode of occurrence of pyrite in thestudied sections is divided into euhedral pyrite and aggregations of framboidal pyrite, of which
the latter are formed around organic matter. These types of pyrite were observed in almost all thehorizons. These modes of occurrence indicate that pyrite formed within the sediment, suggesting a
reductive condition during their diagenesis (Wignall et al., 2010; Bond and Wignall, 2010;
Gallego-Torres et al., 2013; Wang et al., 2013). Measured concentrations of redox-sensitiveelements from bulk samples provide further information on the redox condition. V and U show values
close to average upper continental crust (AUCC) value (Taylor and McLennan, 1985) throughout the
study sections. Mo values are lower than AUCC in most horizons, but slightly high in the middle
part of the Osawa Formation, which is consistent with laminae preservation. Among the modern
examples of various redox conditions (Algeo et al., 2009; Tribovillard et al., 2012), thecombination of U and Mo concentrations in the Osawa Formation is in agreement with those from thedysoxic condition (not sufficiently oxic but not reaching a strong reductive condition).
Accordingly, the depositional environment of the Spathian shallow marine region around the South
Kitakami Microcontinent is regarded as possibly reductive, as suggested by low benthic activity,
and remaining at the level of a dysoxic condition. It is implied that, after the EPME, recovery ofcomplex marine ecosystems during Early Triassic proceeded under such mildly reducing oceanic
environment.

©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-02 -BPT07-02

Japan Geoscience Union Meeting 2016

Keywords: late Early Triassic, South Kitakami, redox condition, Osawa Formation©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-02 -BPT07-03

Japan Geoscience Union Meeting 2016

Paleoenvironmental reconstruction by organic matter analyses of Triassic-Jurassic highly
mature sediments from North America and Inuyama, Japan.
*Yuki Tateshita1, Ken Sawada1, Masayuki Ikeda2
1.Department of Natural History Sciences, Faculty of Science, Hokkaido University, 2.Faculty of
Science, Shizuoka University
Paleoenvironmental reconstruction has been extensively performed using sedimentary organic matter,but paleoenvironmental and paleontological records were hardly preserved in ancient sediments thatare of high maturity. In highly mature ancient sediments, a very small quantity of molecularfossils (biomarkers) in solvent extractable components (bitumen) and insoluble organic matter(kerogen, geomacromolecule) are possibly applicable as paleoenvironmental and paleoecologicaltools. The kerogen has been known to be well preserved as major organic component in ancient
sediment. In the present study, we analyzed Triassic-Jurassic highly mature sediments from North
America and Inuyama, Japan to improve biomarker and kerogen analyses for reconstructing
paleoenvironments, and to examine variations of terrestrial and marine environments during theTriassic-Jurassic.
We used 1) lacustrine sediments (black shales and red sandstones) deposited during
Triassic-Jurassic boundary from North America, and 2) Anisian to Toarcian (T-OAE2) pelagic
sediments (black shales and cherts) of accretionary zone in Inuyama. Whole rock samples werecrushed to a ‘rice’-sized (diameter 2–5 mm) grain in an agate mortar. Crushed rock samples (5–10 g)
were extracted with ultrasonication, by successive treatment with organic solvents. Thereafter,
residues were treated sequentially in a water bath shaker with HCl and HF. We analyzed pyrolysis
and thermochemolysis of kerogen by using GC-MS equipped Curie-point pyrolyzer. Thermochemolysis was
performed with tetramethylammonium hydroxide (TMAH).
Organic matter in sediments from both North America and Inuyama are confirmed to be of highmaturity that were reached oil window. We identified β-carotane (lacustrine algae origin) and2-methyl hopanes (marine cyanobacteria origin) in sediments from North America and Inuyama,
respectively. Interestingly, phenol compounds released from kerogens are mainly detected in blackshale from the East Berlin Formation in Hartford basin. These results suggest that terrestrial
plant-derived materials were more efficiently transported and deposited by environmental change.
Keywords: Triassic-Jurassic boundary, biomarker, kerogen, termochemolysis, highly matured sediment©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-03 -BPT07-04

Japan Geoscience Union Meeting 2016

Environmental change and morphological variability in mid-Cretaceous planktic foraminifer,

Muricohedbergella delrioensis*Eri Takahashi1, Kazuyoshi Moriya1
1.Dep. Earth Sciences, Waseda University
The mid-Cretaceous climate maximum (CCM) (approximately 90–98 Ma) is one of the typical examples of
the green house intervals. Comparing to the modern Earth system, there must be significantly
different interactions between Earth’s surface environment and marine biota in this extreme
condition. Oceanic Anoxic Events (OAEs), which are accompanied by extinction of surface dwelling
microorganisms, e.g. planktic foraminifers, radiolarians, etc., are one of the well known
perturbations in the CCM (e.g. Leckie et al., 2002). The other minor events have also been
identified in the CCM. For example, mid-Cenomanian Event (MCE) is considered as a precursor eventof OAE2 at the Cenomanian/Turonian boundary. However, precise interactions between oceanic surface
environment and planktic foraminifers at the MCE are still poorly understood.
We here examined morphological variability, the maximum diameter and the total number of chambers,of the mid-Cretaceous planktic foraminifers, Muricohedbergella delrioensis, across the MCE. The
specimens were obtained from ODP Site 1258 at Demerara Rise, equatorial Atlantic. Carbon and oxygenisotopic data from the same samples we utilized, published by Moriya et al. (2007), enabled us tocompare our results on morphological variability with those isotopic records. The maximum diameter
becomes smaller in the sequence younger than the MCE, which is accompanied by decrease in the total
number of chambers within a single individual. According to the modern cultivation experiments, themaximum dimeter and the total number of chambers become greater with increase in feeding frequency(Bé et al., 1981). These results indicate that M. delrioensis older than the MCE might have morefeeding opportunity than those younger than the MCE. Additionally, we analyzed a coiling(sinistral/dextral) ratio of M. delrioensis. The coiling ratio shows a significant correlation withthe oxygen isotopic composition, hence temperature. The correlation between the coiling ratio of M
. delrioensis and temperature has also been reported by Desmares et al. (2016). Our resultsreconfirm their implication. Considering modern examples showing genetic discrepancy between
sinistral and dextral morphotypes in the species having a correlation between a coiling ratio andambient temperature (Darling et al., 2006), the coiling direction of M. delrioensis might indicate
existence of potential cryptic (sub)species.
Bé et al., 1981. Jour. Marine Biol. Asso. UK, v. 61, p. 257-277.
Darling et al., 2006. Paleoceanography, v. 21.
Desmares et al., 2016. Palaeogeogr., Palaeoclimatol., Palaeoecol., v. 445, p. 8-17.
Leckie et al., 2002. Paleoceanography, v. 17, 10.1029/2001PA000623.
Moriya et al., 2007. Geology, v. 35, p. 615-618.
Keywords: Cretaceous, Planktic foraminifer, Morphological evolution©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-04 -BPT07-05

Japan Geoscience Union Meeting 2016

Evaluation of ‘paleo’ red-tide during the mid-Cretaceous Oceanic Anoxic Event (OAE) 2.
*Takuto Ando1, Ken Sawada1, Reishi Takashima2, Hiroshi Nishi2
1.Department of Natural History Sciences, Faculty of Science, Hokkaido University, 2.Tohoku
University Museum, Tohoku University
Red-tide is known as blooming of marine phytoplankton, especially dinoflagellate, under
eutrophication, and severely influence on aquatic resources as natural toxins, harmful effects, anddepletion of dissolved oxygen. Moreover, evidence for ‘paleo’ red-tide in the warming period cangive understands for occurrence of red-tide associated with global warming in future.
Dinoflagellate Apectodinium increased during the Paleocene/Eocene Thermal Maximum (PETM)
characterized by global warming (Slujis et al., 2007). However, micropaleontological investigationof dinocyst demonstrated that productivity of dinoflagellate presumably decreased as a result of
the warming during the mid-Cretaceous Oceanic Anoxic Event (OAE) 2 (Pearce et al., 2009).
Paleothermometer such as TEX86 indicate the OAE2 include twice warming and once cooling phases(Forster et al., 2007), and detailed carbon isotope stratigraphy in that interval could enable tocomparison between different localities. In this study, we focus on dinoflagellate biomarker(triaromatic dinosteroid) and very small dinoflagellate-like acritarchs, and compare these trends
between the Yezo Group (YG; Hokkaido, Japan) and Vocontian Basin (VB; SE France) sediments.
Values of dinoflagellate production proxy (triaromatic dinosteroid index; TADS) increase at twice
during the OAE2 interval, the onset of 1st build-up phase and from the Trough to 2nd build-up
phases, in both YG and VB sediments. These results are synchrous with global warming trend
estimated by TEX86 and suggest elevated contribution of dinoflagellate for primary production indifferent two sections located at NW Pacific and Tethys. Huber et al. (1999) reported ‘collapse’ ofvertical stratification during the warming phase of the OAE2. These changes related to global
warming presumably caused enhanced nutrient supply from intermediate and bottom water masses andglobal expansion of suitable condition for dinoflagellate. Moreover, marine palynomorphs are mainlycomposed of very small (< 20µm diameter) spiny acritarchs (Micrhystridium) in the higher TADS
samples in both two sections. It was reported that Micrhystridium-accumulated fraction of theCambrian sediments have high concentration of dinosteane (Talyzina et al., 2000), although theorigin of these acritarchs are uncertain. These acritarchs are similar to Gonyaulacoid dinocyst in
the morphology and smaller than these cysts, which suggest original species of these acritarch areautotrophic and r strategist such as modern red-tide species. From these results, it is impliedthat frequent occurrences of red-tides by small dinoflagellate were triggered by global warming andeutrophication, and promoted efficient deposition of organic matter and consequently expansion ofanoxic water mass.
Keywords: Cretaceous, Dinoflagellate, red-tide, Oceanic Anoxic Events, acritarch©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-05 -BPT07-06

Japan Geoscience Union Meeting 2016

Draught in the low latitudes and cooling by global soot aerosols led to the mass
extinction at the Cretaceous-Paleogene boundary*Kunio Kaiho1, Naga Oshima2, Kouji Adachi2, Yukimasa Adachi2, Takuya Mizukami1, Megumu Fujibayashi3,
Ryosuke Saito1
1.Graduate School of Science, Tohoku University, 2.Meteorological Research Institute, Tsukuba,
Japan, 3.Ecological Engineering Laboratory, Tohoku University
The extinction of the dinosaurs at the Cretaceous/Paleogene boundary led to the macroevolution of
mammals and appearance of humans. The current hypothesis for the extinction of the dinosaurs isthat an asteroid impact at Chicxulub, present-day Mexico, formed condensed aerosols in thestratosphere, which caused the cessation of photosynthesis and global near-freezing conditions.
Here, we propose a new hypothesis that latitude-dependent climate changes caused by the sootaerosols in the stratosphere could consistently explain both the extinction of the dinosaurs andthe survival of the crocodilians. Our geochemical data show that stratospheric soot aerosols wereejected from the oil-rich area by the asteroid impact and spread globally, coinciding with thedevastation of land plants. Our model calculation and biological interpretation indicate that thesoot aerosols caused sufficiently colder climates at the mid–high latitudes for several years,
inducing the extinction of the dinosaurs and crocodilians in those areas. However, the climate
still remained warm enough for their survival and the weak sunlight was still sufficient for plant
photosynthesis at low latitudes, but the substantial decreases in precipitation occurred at low
latitudes over several years resulting in draught, which may have affected their eventual
extinction or survival.
More than 90% species of planktonic foraminifera, which inhibited the global seas, became extinct
coinciding with the asteroid impact at the Cretaceous/Paleogene boundary. Our model calculation
indicates that the soot aerosols caused 7–11°C, 4–8°C, and 3–6°C cooling at most in the 2 m, 50 m,
and 100 m water depths in the low-middle latitude ocean. The rapid global cooling may have caused
the marine extinctions.
Keywords: mass extinction, dinosaurs, planktonic foraminifera, Cretaceous-Paleogene boundary, soot,climate©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-06 -BPT07-07

Japan Geoscience Union Meeting 2016

Ontogenetic stable isotope records of Eocene planktic foraminifers: Comparison to modern
symbiotic species observation*Haruka TAKAGI1, Kazuyoshi Moriya2, Toyoho Ishimura3
1.Graduate School of Creative Science and Engineering, Waseda University, 2.Department of Earth
Sciences, Waseda University, 3.National Institute of Technology, Ibaraki College
Many planktic foraminiferal species in the Eocene epoch are thought to have symbiotic algae in
their cytoplasm. Detection of photosymbiosis is achieved from ontogenetic isotopic signature; the δ13

C of symbiont-bearing species yields more 13C-enriched values than the asymbiotic species,

reflecting selective incorporation of 12C by the symbiont photosynthesis. Because foraminiferal
tests grow intermittently by adding a new chamber on the preformed test, each chamber holds
information of the symbiont photosynthesis at the time of the chamber calcification. Recently, we
have proposed chamber-by-chamber isotope analyses to investigate ontogenetic development of thephotosymbiotic relationship. Here, we show the preliminary results of ontogenetic trends ofisotopic values of Eocene species, and discuss the profiles from our observational results ofcultured modern species.
Three Eocene species recovered by IODP Exp. 342 (U1407) were analyzed to examine ontogenetic
isotopic profiles; Morozovella, Acarinina (symbiotic), and Subbotina (asymbiotic). Each individual
test was dissected into chambers by using a micro-blade, then analyzed by the customized
continuous-flow mass spectrometry system that can measure micro-volume carbonate as small as asingle chamber.
The δ13C values of Morozovella and Acarinina tended to show the ontogenetic positive shifts until
the penultimate chamber. Then the final chamber showed more 13C-depleted δ13C value drastically by
0.5–1.0 ‰. In contrast to these species, Subbotina showed comparatively 13C-depleted δ13C values
whole through its ontogeny. We can say that the progressive 13C-enrichment of the chambers δ13C withgrowth, excluding the last chamber, seen in Morozovella and Acarinina probably reflected theincrease of the effect of symbiont photosynthesis. The contrasting relatively constant δ13C values
through ontogeny seen in Subbotina is in good agreement with the known asymbiotic nature of thisspecies. The notable thing is that the last chamber of the two symbiotic species showed comparable
δ13C value to that of Subbotina. It indicates that the two symbiotic species had already lost their
symbionts, or their photosynthesis was not active at the time of the last chamber calcification.
Our recent culture experiments of modern species (Globigerinoides sacculifer and Globigerinella

siphonifera) to investigate symbiont photosynthesis through ontogeny showed that the chlorophyll
content of the foraminifers, thus the symbiont content, drastically decreased to almost zero at thetime or just before the gametogenesis. It sometimes occurred during the last chamber calcification.
These modern observations indicate that the more 13C-depleted δ13C value in the final chamber in
Eocene symbiotic species could reflect the digestion or lysis of symbionts. If so, it can be said
that each individual had to acquire the symbionts from the environment at some time during the
ontogeny as the modern obligate symbiotic species do.
Keywords: Eocene, Planktic foraminifer, Carbonate stable isotopes, Photosymbiosis©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-07 -BPT07-08

Japan Geoscience Union Meeting 2016

Radiolarian faunal turnover across the early/middle Miocene boundary in the easternequatorial Pacific Ocean*Shin-ichi Kamikuri1
1.Faculty of Education, Ibaraki University
The lower to middle Miocene sequence was drilled at IODP Site U1335 (5°18.735’N, 126°17.002’W,
water depth 4328 m) in the eastern equatorial Pacific Ocean. In the modern ocean, Site U1335 is
located under the North Equatorial Current, and the biogenic silica fluxes to the sea-floor
sediments are comparatively high in this area. The sediments recovered from Site U1335 are
predominantly nannofossil ooze with siliceous microfossils such as diatoms and radiolarians.
230 morphotypes of radiolarians were identified at this site. Because the low latitude species
commonly occurred at this site, the tropical Cenozic zonation of radiolarians proposed by
Sanfilippo and Nigrini (1998) was adopted. The studied sequence was divided into four zones,
consisting of the RN2 (the Stichocorys delmontensis Interval Zone), RN3 (the Stichocorys wolffii
Interval Zone), RN4 (the Calocycletta costata Interval Zone), and RN5 (the Dorcadospyris alataInterval Zone) at Site 1335. In the standard zonal scheme, the early/middle Miocene boundary
corresponds to the top of C5Cn.1n with an age estimate of 16.268 Ma (Pälike et al., 2010; Gradstein
et al., 2012). Hence, this boundary was placed at 189.6 mcd at Site 1335.
Radiolarian fauna was divided into three assemblages based on variations in the composition of
dominant species: an early Miocene assemblage (20.0 to 16.8 Ma), a transitional assemblage (16.8 to
13.4 Ma) and a middle Miocene assemblage (13.4 to 12.0 Ma). The early Miocene assemblage ischaracterized by two dominant species of S. delmontensis, S. wolffii, and Tholospyris anthophora.
The transitional assemblage consists of three dominant species of S. delmontensis, Calocycletta

robusta group, and T. anthophora. The four dominant species of the middle Miocene assemblage
present in this assemblage are Stylodictya sp. A, Lophocyrtis aspera, Disolenia spp. andCollosphaera spp. The most significant faunal turnover of radiolarians is marked at the boundary
between the transitional/middle Miocene assemblages.
Keywords: radiolaria, Miocene, eastern equatorial Pacific©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-08 -BPT07-09

Japan Geoscience Union Meeting 2016

Geologic age of the whale fossil-bearing calcareous float concretion from the Hae River,
Hokkaido, Japan, based on radiolarian and diatom analyses*Isao Motoyama1, Toshiaki Maruyama1, Tomohiro Nishimura2, Kazuhiko Sakurai2, Akane Kasukawa1, Kenji
M. Matsuzaki3
1.Department of Earth and Environmental Sciences, Yamagata University, 2.Hobetsu Museum,
3.Geological Survey of Japan, AISTRadiolarian and diatom fossils have been used to constrain the age of calcareous concretion
collected from the Hae River, Hidaka Town, southern central Hokkaido, Japan. The calcareous
concretion contains whale fossils and was discovered as a float during the riparian works in 2005.
Recovered radiolarian and diatom assemblages indicate the Lipmanella redondoensis Zone (9.0 to 7.4
Ma) and the Rouxia californica Zone (7.7 to 6.5 Ma), respectively. Thus the concretion can be dated
as 7.7 to 7.4 Ma. This age is concordant with the age range of the Nina Formation which is
distributed near the locality of the concretion and was previously dated as ca. 10.1 to 3.5 Ma
based on the diatom stratigraphy in the surrounding area. We will examine some samples collectedfrom the Nina Formation exposed along the Hae River to confirm the origin of the concretion.
Keywords: whale fossil, Radiolaria, Diatom©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-09 -BPT07-10

Japan Geoscience Union Meeting 2016

The extinct pinniped Allodesmus (Mammalia: Carnivora) from the Miocene of Hokkaido,
northern Japan, and its implications for phylogeny and postcranial morphology*Wataru Tonomori1, Hiroshi Sawamura2, Tamaki Sato3, Naoki Kohno1,4
1.Graduate School of Life and Enviromental Sciences, University of Tsukuba, 2.Ashoro Museum ofPaleontology, 3.Department of Astronomy and Earth Sciences, Tokyo Gakugei University, 4.Departmentof Geology and Paleontology, National Museum of Nature and Science

Allodesmus is an extinct pinniped that is known from the Middle and Late Miocene of the North
Pacific and belongs in the family Desmatophocidae, which became extinct in the early Late Miocene.
According to the previous studies, Allodesmus has at least five species and is divided into threesubgroups: i.e., “Basal”, “Broad head” and “Long head” subgroups. However, the phylogenetic studyof Allodesmus has been limited until now, and therefore, the evolutionary history of theDesmayophocidae is also still unclear. Moreover, a study of postcranial bones of Allodesmus nor
the Desmatophocidae is almost nothing because of insufficient skeletal material for those taxa.
In this study, we described a specimen of Allodesmus (AMP25) collected in 1991 from the Middle
Miocene Okoppezawa Formation, Hokkaido, northern Japan. AMP25 contains 83 bones consisting of askull, fore- and hind-limbs, ribs and vertebrae. To demonstrate the paleobiological importance of
this specimen, we performed cladistic analysis to locate the new specimen in the phylogenetic
framework. We used PAUP 4.0 and Mesqueite 3.03, and then, we based on 97 morphological charactersand 15 species, with the enigmatic musteloid Potamotherium, and the basal pinnipeds Enaliarctos
and Pteronarctos as out-group.
As a result, previously recognized “Long head” subgroup was supported as a monophyletic group, but
the “Broad head” subgroup was not recognized as a monophyletic group in our analysis. As for AMP25,
it didn’t have any synapomorphy of the “Long head” subgroup and nested with Allodesmus packardi and
A. naorai as unresolved polytomy. On the other hand, AMP25 has an autoapomorphy in that the
supraorbital process is located at the anterior portion of the interorbital bar in our analysis.
From the above and additional observations, we have concluded that AMP25 belongs to an unknown
species. Importantly, some postcranial bones of AMP25 also show very different character
combination, differentiating it from A. kernensis among the Desmatophocidae. In particular,
morphology of the calcaneum (that is one of the component of the ankle bones) of AMP25 isremarkably distinguishable from that of A. kernensis. For example, the calcaneum of AMP25 is more
slender than that of A. kernensis, and its peroneal tubercle is more developed than that of A.
kernensis. These characters were distinguishable not only among the species of Allodesmus but among
all other pinnipeds. It means that some postcranial characters other than characters that we used
for the phylogenetic analysis in this study also have potential phylogenetic values as well as its
functional importance.
Keywords: pinnipeds, Allodesmus, phylogeny, postcranium©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-10 -BPT07-11

Japan Geoscience Union Meeting 2016

Evaluation of early diagenetic influence on nitrogen isotopes within fossil amino acids:
Towards estimation of ancient food webs
*Daijiro Hagehashi1, Robert Jenkins2, Akiko S. Goto2, Yoshito Chikaraishi3, Takashi Hasegawa2
1.Division of Environmental Science and Engineering, Graduate school of Natural Science andTechnology, Kanazawa University, 2.School of Natural System, College of Science and Engineering,
Kanazawa University, 3.Japan Agency for Marine-Earth Science and Technology
Compound-specific isotope analysis (CSIA) of nitrogen within amino acids is a relatively new tool
to estimate the tropic level of organisms (Chikaraishi et al. 2009; Limnol Oceanogr Meth). It would
be applicable as a new technique to the trophic and ecological study of fossils. Hard parts (e.g.
shells and bones) usually contain amino acids, which can be extracted and identified in a number ofprevious studies. However, amino acids in fossils would be influenced by diagenesis, including
thermal maturation, racemization, and degradation. Thus, it is important to evaluate whether or not
the amino acids within the shell keep the original isotopic composition of organisms. Thus, thisstudy aim to evaluate consistency of the estimated trophic level based on the CSIA of amino acidsin shells with respect to early diagenesis. We use modern and fossil Turbo cornutus (Gastropoda),
which is presumably primary consumer, i.e. trophic level should be 2.0. Fossil Turbo were obtained
from Yuigahama archaeological site (Kanagawa Pref., Kamakura Era, 13-14th century, ca. 800 yearsago) and Torihama archaeological site (Fukui Pref., Jyomon Era, ca. 4000 years ago). The modernmaterials were obtained from Hakui, Ishikawa and Kaneda, Chiba. Some of the modern materials were
heated at 200 and 400 °C in oven.
Prior to the isotope analysis, the samples were examined in several ways, including X-ray
diffraction pattern analysis, SEM observations of shell microstructures, D/L ratio of amino acids
within the shells to evaluate the preservation of the samples. Turbo cornutus shell was composedof three layers. Our observation reveal that the outer layer of the shell contaminated by
encrusting biota. Middle layer, consists of nacreous structure, sometimes had erosion by microbes.
Moreover, microstructures of the modern sample heated at 400 °C were partially dissolved andrecrystallized, and no amino acid was found in there. Amino acid composition in these aged samples
was similar to the clean modern ones. Based on those results, we used several fossil samples, which
remained original microstructures, for the isotope analysis. We also analyzed modern samples,
including those heated at 200 °C and invaded by microbes.
As a result, all the samples analyzed show around 1.9-2.3 for the trophic level estimated based on
the CSIA of amino acids. It is indicated that the early diagenesis wouldn’t affect to the nitrogenisotopes of amino acids in shells at least for 4000 years.
Keywords: Trophic level, fossil, amino acids, stable nitrogen isotope ratios, early diagenesis©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-11 -BPT07-12

Japan Geoscience Union Meeting 2016

Effects of carbonate chemistry and metabolism induced by ocean acidification on stable
isotope fractionation in molluscan shell carbonate*Kozue Nishida1,2, Masahiro Hayashi3, Akari Nagoshi4, Hodaka Kawahata4, Mizuho Sato1,5, Atsushi Suzuki
1

1.National Institute of Advanced Industrial Science and Technology, 2.The University Museum,
UTokyo, 3.Marine Ecology Research Institute, 4.AORI, UTokyo, 5.Asahi Geo-Survey Co. Ltd
Stable oxygen and carbon isotope compositions of biogenic carbonate have been widely used for many
paleoclimate, paleoecological, and biomineralization studies. Oxygen isotope compositions ofcarbonate, a commonly used proxy of seawater temperature and oxygen isotope compositions ofseawater, are also affected by seawater carbonate chemistry, but the knowledge of its dependency on
stable isotope fractionation of both synthetic and biogenic aragonite is still limited. It has also
been reported that carbon isotope compositions of molluscan shells are affected by carbon isotope
compositions of seawater carbonate chemistry and metabolic carbon. Several studies reported effectsof ocean acidification on metabolism of molluscs, and thus the metabolic changes could potentiallyinfluence the stable isotope compositions of metabolic carbon. Here, we have focused on stable
oxygen and carbon isotopic responses of moluscan shells to CO2-driven seawater acidification forunderstanding of the contribution of environmental and metabolic effects. Two species of clams (Scapharca broughtonii, Pseudocardium sachalinense) and two species of abalones (Haliotis discus
discus, Haliotis gigantea) were cultured in seawater chemically manipulated to vary pCO2 condition
using CO2 control system of the Demonstration Laboratory, Marine Ecology Research Institute (MERI),in Kashiwazaki City, Niigata Prefecture, Japan.
Stable oxygen isotope compositions of S. broughtonii had significant negative correlations with pH(-0.48‰ /pH, at 17°C; -0.61‰ / pH, at 25 °C). These of P. sachalinense, H. discus discus, and H.

gigantea showed non-significant relationships with pH and small variations (within 1 per mil). The
oxygen isotope fractionation in four species of our study are smaller than that of synthetic
calcite (-1.42‰ / pH, Zeebe et al., 1999).
The significant negative correlations between stable carbon isotope compositions and pH appeared in

S. broughtonii, H. discus discus, and H. gigantea which had non-significant pH effects on
calcification, and the slopes of these relationships of shell carbonate were lower than these of
dissolved inorganic carbon (DIC) of seawater. We estimated the equilibrium values of carbon isotope
compositions at each pCO2 treatment, and the difference between the carbon isotope compositions ofshell carbonate and equilibrium values showed gradual increases of carbon isotope values withdecreasing pH in S. broughtonii, H. discus discus, and H. gigantea. Thus, the pCO2-induced change
in metabolism might appear in carbon isotopes of shells of these species as the metabolic effect.
On the other hand, in P. sachalinense which showed a decrease in calcification in our culture
experiment of ocean acidification, the difference between the carbon isotope compositions of shellcarbonate and equilibrium values did not indicate a significant pH dependency. This result might be
attributable to differences in metabolic responses to acidified seawater.
The findings of our study will contribute to the correction of isotopic paleotemperature ofbiogenic carbonate and the understanding of acidification effects on metabolism of marine
calcifiers.

©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-12 -BPT07-12

Japan Geoscience Union Meeting 2016

Keywords: ocean acidification, stable isotopes, mollusca, biomineralization, proxy, pH©2016. Japan Geoscience Union. All Right Reserved.

- BPT07-12 -