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Article type: Cover
1996 Volume 60 Pages
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Article type: Appendix
1996 Volume 60 Pages
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Article type: Appendix
1996 Volume 60 Pages
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Article type: Index
1996 Volume 60 Pages
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Article type: Appendix
1996 Volume 60 Pages
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Hitoshi Furusawa
Article type: Article
1996 Volume 60 Pages
1-11
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New material of sirenian fossil was recognized from the upper Miocene of Numata-cho, Hokkaido, Japan. This specimen belongs to the genus Dusisiren of the subfamily Hydrodamalinae, because of its size of vertebrae and ribs. Another genus of the Hydrodamalinae, Hydrodamalis spissa, has been found from the lower Pliocene of this area before (Furusawa et al., 1990). Detailed relationship of these specimens and the evolution of North Pacific sirenia may be clear by new specimens from this region in the future.
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Yasumitsu Kanie, Mutsuo Hattori, Kazumi Akimoto, Ryuichi Majima
Article type: Article
1996 Volume 60 Pages
12-
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Mutsuo Hattori, Yasumitsu Kanie, Tadamichi Oba, Kazumi Akimoto
Article type: Article
1996 Volume 60 Pages
13-22
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Methane (biogenic)-rich cold seepage zones are distributed along the N-S trend active fault off Hatsushima Island and NW-SE trend active fault along the foot of Okinoyama Bank Chain in the western and central parts of Sagami Bay, the depth ranging from about 800m to 1450m. The Philippine Sea Plate is subsiding beneath the North American Plate and lzu Peninsula along those active faults. Chemosynthetic animal communities and carbonates are widely distributed along the cold seepage zones. The δ^<13>C and δ^<18>O values of carbonates range from -27 to -38‰ vs PDB and from 3.24 to 6.42‰ vs PDB respectively. The CaCO_3 and MgCO_3 contents of carbonates range from 34 to 89% and from 13 to 16% respectively. The ^<14>C ages of two Calyptogena shells included in carbonates are 9710±100 and 37020±1060 yBP. High temperatures as much as 11.5℃ of bottom sediments about 20cm below the bottom surface were observed at the reddish brown colored bacteria mat area, whereas the temperature of bottom water is around 3℃. Temperatures of the bottom sediments about 20cm below bottom surface in Calyptogena communities are at about 2 to 3℃ higher than the temperature of bottom surface water. It is clarified that the environmental conditions of the reddish brown colored area and the area of Calyptogena communities differ in temperature, texture, pH, oxygen contents of bottom sediments, composition of carbonates and combination of chemosynthetic animals.
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Shigeaki Kojima, Suguru Ohta, Jun Hashimoto
Article type: Article
1996 Volume 60 Pages
23-25
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The phylogenies of species of the genus Calyptogena and vestimentiferans collected from the seep areas in the Sagami Trough and the Nankai Trough were analyzed on the basis of partial nucleotide sequences of mitochondrial DNA. The geographical distribution of Calyptogena was generally narrow and many endemic species were sampled from single sites. In contrast, species of vestimentiferan were distributed over wider geographical ranges and their dispersion was tend to be limitted by water depth rather than by horizontal distances. Difference of distribution pattern between two groups is thought to be attributed to the difference in the larval dispersive ability.
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Takeshi Naganuma, Mutsuo Hattori, Jun Hashimoto, Yasumitsu Kanie
Article type: Article
1996 Volume 60 Pages
26-31
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Tubes of living vestimentiferan worms were collected from a deep-sea cold seep and a submarine volcanic vent. Both habitats were characterized as chemically reductive conditions with high concentrations of hydrogen sulfide and methane. The cold seep site was also characterized by the formation of carbonate rocks such as high-magnesium calcite, to which vestimentiferan tubeworms anchored. Magnesium and calcium were concentrated on the surfaces of worm tubes, as revealed by the electron-probe X-ray microanalysis on the worm tube cross-sections. Iron, phosphorus and other minor elements were present mostly on the surfaces, but the distributional patterns were different from those of magnesium and calcium. Only sulfur accumulated inside of the tube material. The elemental distributions may be explained by the coupled processes of methane oxidation, sulfate reduction (=sulfide formation) and carbonate formationn, in the tubeworm habitats or in the tubeworm tissues.
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Toshiyuki Masuzawa
Article type: Article
1996 Volume 60 Pages
32-40
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Pore water samples were collected with an in situ pore water squeezer for a submersible (ISPS-S) by the submersible Shinkai 2000 from a Calyptogena patch in the largest living Calyptogena community at the Hatsushima site (34°59.9'N, 139°13.6'E; 1146m deep) in western Sagami Bay, Japan. Sulfate decreased remarkably below 9cm depth and showed very low minimum values between ca. 20 and 40cm depth. Inversely, hydrogen sulfide increased significantly below 9cm depth and showed a very high maximum value of 13.8 mM at 36cm depth. DIC increased remarkably with hydrogen sulfide, and its δ^<13>C values decreased remarkably to less than -40‰. These indicate that microbial sulfate reduction using methane as the reductant proceeds actively at depths of ca. 20 to 40cm below the sediment water interface just beneath the living giant clams. Based on chemical and isotopic data of pore waters, geochemical situations of the Calyptogena communities at the Hatsushima site have been discussed.
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Kazumi Akimoto, Tomoe Saji, Reiko Tsutsumi, Ena Yoshihara
Article type: Article
1996 Volume 60 Pages
41-47
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This report discusses the relationship between benthic foraminiferal species and the chemical character of the bottom and interstitial waters in the habitat of the Calyptogena community (139°13.6'E, 34°59.9'N, 1160m in water depth) off Hatsushima Island of Sagami Bay. Thirty one sediment samples, which were reported the chemical characters of the interstitial water by Masuzawa et al. (1992), are used for this benthic foraminiferal analysis. Four species such as Bulimina aculeata, Bulimina striata, Cibicidoides mediocris and Rutherfordoides cornuta abundantly occur in those samples. Distribution patterns of these four species are dipcited through the Q-mode factor anaysis. Those of B. striata and R. cornuta are closely related with the metane contents of the bottom water. B. striata is considred to be tolelant of high hydrogen sulfide conditions.
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Hiroshi Kitazato
Article type: Article
1996 Volume 60 Pages
48-52
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Faunal characteristics and adaptations of benthic foraminifera associated with cold seepages are discussed. A few species are known from cold seepages where an anoxic environment was produced due to methane or hydrogen sulfide gas. Neither of the two species in Sagami Bay is endemic to the seepages : one is common even in oxic bottom, and the other is present in anoxic microenvironments below the surface oxic layer. There are two possibe explanations for the survival of benthic foraminifera in anoxic/euxinic cold seepage environments. First, some foraminifera may be able to tolerate anoxic environments, using anaerobic respiration system. However, in this case, the foraminiferal tests should dissolve due to organic acids produced during anaerobic respiration. Second, foraminifera may be in symbiosis with sulfide oxidizing bacteria. Larger chemosynthetic animals house sulfide oxidizing bacteria. It is possible that foraminifera can also house bacteria in their cells, although up to the present time few foraminifera have been reported to have such bacteria. Of the two ideas, I believe the second is more likely to be true, and in this contribution I explore the possibility of sulfide oxidizing bacterial symbionts in cold seepage foraminifera.
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Yasumitsu Kanie
Article type: Article
1996 Volume 60 Pages
53-58
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Chemosynthesis-dependant benthic fossil assemblages have been known to occur at the ten horizons (18-0.5Ma) of Miura-Boso area (Table 1). The assemblages of the middle Miocene Hayama Formation (15Ma) consists mainly of Acharax, Calyptogena, Lucinoma, Cochocele, tube-worms articulates of Decapoda, etc. These fossils were found along the fault-claystone and -breccia, and were frequently preserved in carbonate concretions. The faunal characteristics as well as lithologic and tectonic settings of the fossil-bearing deposits are compared to those of the chemosynthesis-dependant behthic communities in the Sagami Trough. Therefore, the fault zone in the Hayami Formation is regarded as located in the subduction zone in middle Miocene time. The most dominant species of the assemblages is Acharax yokosukensis, whose habitat is correlated with the middle bathyal zone of chemosynthetic muddy infauna. The paleodepths of the Hayama Formation indicated by benthic foraminifers suggest a middle bathyal zone (1200-1600m in depth), being correlated well with the habitat of Calyptyogena-community of the Sagami Trough. The habitat of the fauna was assumed to be substrata where the seepage of methane-bearing water was supplied. Comparison of the fossil assemblages with extant Calyptogena communities suggests historical changes of the paleoenvironmental settings of the Miura and Boso Peninsulas from the boundary between the continental and ocean plates in the Middle Miocene (15Ma) to the middle part of the middle bathyal zone of modern Sagami Trough since Pliocene (3.5Ma) through the continental border in upper abyssal to lower bathyal zone in Late Micoeone time (ca. 12Ma).
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Tatsuro Matsumoto
Article type: Article
1996 Volume 60 Pages
59-62
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Tetsuro Hanai
Article type: Article
1996 Volume 60 Pages
63-66
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Kenshiro Ogasawara
Article type: Article
1996 Volume 60 Pages
67-
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Kei Mori
Article type: Article
1996 Volume 60 Pages
68-69
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Article type: Appendix
1996 Volume 60 Pages
70-79
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Article type: Bibliography
1996 Volume 60 Pages
80-81
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Article type: Appendix
1996 Volume 60 Pages
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1996 Volume 60 Pages
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Article type: Appendix
1996 Volume 60 Pages
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Article type: Appendix
1996 Volume 60 Pages
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1996 Volume 60 Pages
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1996 Volume 60 Pages
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1996 Volume 60 Pages
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1996 Volume 60 Pages
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1996 Volume 60 Pages
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1996 Volume 60 Pages
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1996 Volume 60 Pages
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1996 Volume 60 Pages
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1996 Volume 60 Pages
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Article type: Cover
1996 Volume 60 Pages
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1996 Volume 60 Pages
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