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2007 Volume 81 Pages
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2007 Volume 81 Pages
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Article type: Appendix
2007 Volume 81 Pages
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2007 Volume 81 Pages
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Yoshiki Koda, Wataru Koike, Hisao Ando, Teruya Uyeno, Kazuyuki Usui
Article type: Article
2007 Volume 81 Pages
1-2
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Article type: Index
2007 Volume 81 Pages
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2007 Volume 81 Pages
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Hiroyuki Takata, Ritsuo Nomura, Koji Seto
Article type: Article
2007 Volume 81 Pages
5-14
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Paleoceanographic condition in the deep-sea ocean during the Eocene-Oligocene transition is affected by change in ice volume in the Antarctic region and deep-water formation in the Southern Ocean. ODP Leg 199 in the eastern equatorial Pacific Ocean recovered continuous sections containing well-preserved microfossils during the Eocene-Oligocene interval, and provides an opportunity to study this transition. In this paper, we review recent results of the Oligocene paleoceanography and outlines of faunal change in benthic foraminifers in the eastern equatorial Pacific Ocean. Sedimentary records from ODP Leg 199 represent a deepening of calcite compensation depth (CCD) more than 1 km near the Eocene/Oligocene boundary in the eastern equatorial Pacific Ocean. Around the interval of CCD change, two-step positive sifts of oxygen isotope occurred in benthic foraminifers within〜300kyrs. The glaciation events marked by the Oil isotope event coincide with the intervals of low eccentricity and low obliquity amplitude variations, due to absence of warm summer. Other three glacial events of 29.16, 27.91 and 26.76 Ma during the Oligocene are probably related to low obliquity amplitude variation fluctuating with about a 1200 kyr.-cycle. Abyssal benthic foraminifers show an increase in Antarctic-bottom water fauna (Nuttallides umbonifer) around the Early/Late Oligocene boundary in the eastern equatorial Pacific Ocean. The short-term abundance peaks of Nuttalides umbonifer are correlative with the Oi event, suggesting that this species could be useful as a proxy of the Antarctic ice-sheet expansions.
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Kazuko Usami, Shiro Hasegawa, Tatsuhiko Sakamoto, Koichi Iijima, Tadam ...
Article type: Article
2007 Volume 81 Pages
15-23
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Pleistocene-Holocene assemblages of benthic and planktonic foraminifera from Hole 969F (Mediterranean Ridge) and Hole 967D (Eratosthenes Seamount) of ODP Leg 160 were examined to reconstruct the paleoenvironmental changes during deposition of sapropels (S1, S3〜S7) over the last 200 kyr in the Eastern Mediterranean. On the benthic assemblages, three major species are dominant throughout the two cores, except for the sapropel horizons where benthic foraminifera are nearly absent, suggesting an anoxic bottom environment. A Q-mode factor analysis of planktonic foraminifera has extracted four varimax assemblages. The factors 1 and 3 correspond to warm and cool waters, respectively. Both the factors 2 and 4 show low-saline coastal waters. The factor 2 indicates enhanced fertility in surface water, and the factor 4 indicates warmer and low salinity water than other factors. Factor loading of factor 4 increases in sapropel layers from S3 to S7, while the factors 1 and 2 display relatively long-term periodicities and are not related to times of sapropel formation. During the sapropels deposition from S3 to S5 and S7 in the interglacial intervals, the Eastern Mediterranean was stratified due to a cover of fresh and warm surface water inferred by the factor 4 and its ventilation in deeper water was reduced. The sapropel S6 formed in glacial period, and stratification in the surface water is relatively weak. However, the enhanced productivity may supply abundant organic matters to the sea floor. In the sapropel S1, spatial variability of paleoceanographic environment, which is recognized in this work, may be useful to understand the causes of sapropel formation.
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Yuji Takakuwa
Article type: Article
2007 Volume 81 Pages
24-44
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Accumulating fossil records of deep-sea sharks are important for reconstruction of their paleoecology and evolution, because these fossils are generally rare everywhere in the world. This paper reports the newly discovered and diverse fossil assemblage of deep-sea sharks from the Miocene deposits in the southwestern part of Gunma Prefecture, central Japan. The specimens are isolated teeth found from seven localities of three Middle Miocene formations. These fossils are identified into twelve species of eleven genera belonging to eight families within three orders: eight species from the Obata Formation (earliest Middle Miocene) of the Tomioka Group, six species from the Haratajino Formation (early Middle Miocene) of the Tomioka Group and four species from the Niwaya Formation (middle Middle Miocene) of the Annaka Group. Four genera, Centrophorus, Deania, Squaliolus and Mitsukurina represent the first fossil record in the Northwest Pacific. Somniosus and Centroscymnus mark the second record from the Miocene in the world, and Etmopterus and Pseudocarcharias indicate the second in the circum-Pacific. On the basis of lithofacies, benthic foraminifers and other megafossils, three formations are thought to have been deposited under outer sublittoral to middle bathyal environments. Since these environments accord with the Recent species habitats of the eleven shark genera, this fossil deepsea shark fauna similar to the recent one in species/generic composition had been habited in bathyal environment. The presence of this Miocene fauna suggests that the outline of the recent deep-sea shark fauna in the Northwest Pacific region would have been already established the Miocene. The establishment of the fauna might have been resulted from the vicariance and the isolation that caused by the closure of Indonesian seaway and its associated expansion of shallow sea in the Oligo-Miocene time.
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[in Japanese], [in Japanese]
Article type: Article
2007 Volume 81 Pages
45-
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Jun-ichi Tazawa
Article type: Article
2007 Volume 81 Pages
46-56
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H. Yabe, who, in 1900, described Leptodus from the Permian of the southern Kitakami Mountains, northeast Japan, initiated the study of Japanese Palaeozoic brachiopods. This paper is a review of two hundred-seven articles published between 1900 and 2006 about Silurian, Devonian, Carboniferous and Permian brachiopods from Japan.
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Kazuyoshi Endo
Article type: Article
2007 Volume 81 Pages
57-66
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Recent hypotheses regarding the origin and body plan evolution of brachiopods are reviewed. Brachiopods are firmly placed within the lophotrochozoa, one of three major bilaterian lineages revealed by molecular phylogeny. Comparisons of mitochondrial gene arrangements further suggest that brachiopods are closer to annelids than to molluscs, a scheme supported by morphological comparisons of Cambrian fossils, including those of halkieriids and wiwaxiids. Any scenario explaining the brachiopod origin may involve curling of the dorso-ventral axis along the anterior-posterior axis. This hypothesis could partly be tested by methods of molecular developmental biology. Some potential pitfalls of this approach are discussed with reference to the deuterostome-like features of brachiopods and to the ubiquity of co-option of developmentally important genes.
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Kazuyuki Yamamoto, Yasufumi Iryu, Tsutomu Yamada
Article type: Article
2007 Volume 81 Pages
67-78
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Stable carbon and oxygen isotopes in skeletal carbonates are powerful tools for reconstructing various paleoenvironmental conditions. Of many marine invertebrates, articulated brachiopods have been preferentially used as a reliable recorder of carbon and oxygen isotopic compositions in the past oceans because: (1) their dense, low-magnesium calcite shells are less susceptible to diagenetic alteration, (2) their calcitic secondary shell layer is assumed to have been precipitated in or near isotopic equilibrium with ambient seawater, and (3) they have extensive geographic distributions throughout the Phanerozoic. Recent investigations, however, have demonstrated that previously proposed criteria to identify diagenetic alteration in fossil brachiopod shells are not unequivocal and that the secondary shell layer of some living brachiopods is not precipitated in isotopic equilibrium with ambient seawater due to kinetic and/or metabolic effects. However, these results argue against a general rejection of availability of isotopic compositions of brachiopod shells as paleoenvironmental proxies. Further geochemical investigations are needed to reveal temporal and spatial variations in isotopic compositions within brachiopod shells for evaluating kinetic and/or metabolic effects and to clarify isotopic modifications due to diagenetic alteration.
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Yukihide Matsumoto, Ryo Hashimoto
Article type: Article
2007 Volume 81 Pages
79-85
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Tadashi Sato
Article type: Article
2007 Volume 81 Pages
86-89
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Rei Nakashima
Article type: Article
2007 Volume 81 Pages
90-98
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Yasuhiro Hikichi, Yukihiro Takaizumi, Yutaro Suzuki
Article type: Article
2007 Volume 81 Pages
99-103
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Article type: Appendix
2007 Volume 81 Pages
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[in Japanese]
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2007 Volume 81 Pages
105-
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[in Japanese]
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2007 Volume 81 Pages
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[in Japanese]
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2007 Volume 81 Pages
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[in Japanese]
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2007 Volume 81 Pages
106-107
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2007 Volume 81 Pages
107-109
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2007 Volume 81 Pages
110-113
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113-114
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2007 Volume 81 Pages
114-115
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2007 Volume 81 Pages
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