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Hokkaido University Collection of Scholarly and Academic Papers (135.521 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

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Mostrando recursos 1 - 19 de 19

  1. 北海道夕張-芦別地域に分布する空知層群・蝦夷層群の層序と堆積環境

    高嶋, 礼詩; 吉田, 武義; 西, 弘嗣
    北海道の夕張-芦別地域に分布する最上部ジュラ系~下部白亜紀の空知層群は, ピクライトおよび安山岩質からデイサイト質の火山砕屑岩類を主体とし, 大陸地殻起源のアルコース質砂岩を伴う.これに整合に累重する白亜系蝦夷層群は, 陸源の砂岩・泥岩からなり, 石灰岩ブロックを含むオリストストロームと珪長質凝灰質砂岩層の2つの特徴的な堆積物を挟在する.空知層群下部は, 従来, 無斑晶質の玄武岩が卓越するとされてきたが, 本地域では全てピクライトで, それに安山岩質とデイサイト質の火山砕屑岩, アルコース質砂岩を挟在する.また, 空知層群は深海底の堆積物とされていたが, ウーライト石灰岩を伴うことから堆積場の一部は浅海域であったことが示唆される.

  2. Recent Advances in Research on Terrestrial and Marine sequences from the mid-Cretaceous Oceanic Anoxic Events (OAEs).

    Takashima, Reishi; Gautam, Pitambar; Nishi, Hiroshi

  3. Recent Advances in Research on Terrestrial and Marine sequences from the mid-Cretaceous Oceanic Anoxic Events (OAEs).

    Takashima, Reishi; Gautam, Pitambar; Nishi, Hiroshi

  4. Greenhouse world and the Mesozoic Ocean

    Takashima, Reishi; Nishi, Hiroshi; Huber, Brian T.; Leckie, R. Mark

  5. ヒマラヤ山脈のテクトニクスと東アジアの古環境・古気候の変動

    西, 弘嗣; 高嶋, 礼詩
    The Indian subcontinent and Asian continent first contacted in the late Cretaceous (about 65Ma) and strongly collided after 52Ma because northward motion of the Indian Subcontinent slowed from 18-20cm/yr to 4.5cm/yr. Although the first record of uplift in Himalayan regions has been recorded during the Eocene. Major uplifts of the Himalayan Range and Tibetan Plateau and following sediment supply started from Oligocene through Miocene. Particularly, the rapid uplift stages of Himalayan-Tibetan regions have been recognized, at least. Around 8Ma and the last 1Ma based on sedimentological studies of marine terrestrial sequences. The micropaleontological studies in marine sequences revealed that the...

  6. Planktonic foraminiferal zonation in the Cretaceous Yezo Group, Central Hokkaido, Japan

    Nishi, Hiroshi; Takashima, Reishi; Hatsugai, Takayuki; Saito, Tsunemasa; Moriya, Kazuyoshi; Ennyu, Atsuhito; Sakai, Toshiaki
    The mudstone of the Yezo Group exposed in Central Hokkaido yields abundant microfossils of calcareous nannofossils, foraminifers, radiolarians and dinoflagellates. Benthic foraminifers consisting of both agglutinated and calcareous species occur abundantly and consistently throughout the sequence, while specimens of planktonic foraminifers are generally fewer than benthics in all samples. We recognized the following 13 planktonic foraminiferal zones assigned to the late Aptian to early Campanian in the Oyubari and Haboro–Kotanbetsu areas; (1) Globigerinelloides spp., (2) Ticinella primula, (3) Biticinella breggiensis, (4) Rotalipora subicinensis–Rotalipora ticinensis, (5) Rotalipora appenninica, (6) Rotalipora globotruncanoides, (7) Rotalipora cushmani (8), Whiteinella archaeocretacea (9) Helvetoglobotruncana helvetica, (10)...

  7. Geology, petrology and tectonic setting of the Late Jurassic ophiolite in Hokkaido, Japan

    Takashima, Reishi; Nishi, Hiroshi; Yoshida, Takeyoshi
    The Gokurakudaira Formation, which has a N–S zonal distribution within a latest Jurassic greenstone belt in Hokkaido Island, Japan, constitutes the uppermost ultramafic–mafic unit of the Horokanai Ophiolite. The following three hypotheses for the origin of the ophiolite have been proposed: (1) a mid-oceanic ridge; (2) an oceanic plateau; and (3) an island arc. The Gokurakudaira Formation can be subdivided into four zones extending NNW to SSE, from east (Zone I) to west (Zone IV), based on lithofacies and areal distribution. Zones I and III consist of aphyric tholeiite resembling back-arc basin basalt (BABB), while Zone II is characterized by...

  8. 東京大学北海道演習林地域に分布する中生界空知層群および蝦夷層群の層序と地質

    高嶋, 礼詩; 宮本, 義憲; 西, 弘嗣; 吉田, 武義
    要旨: 東京大学北海道演習林地域には上部ジュラ-白亜系空知層群および蝦夷層群が分布する。本地域の空知層群は、下位より玄武岩主体の極楽平層、筑紫岳マイクロモンゾナイト、礫岩、砂岩、泥岩からなる布部層、玄武岩主体で珪質泥岩を伴う小黒瀬層、泥岩と珪長質凝灰岩からなる麓郷層に区分される。このうち、筑紫岳マイクロモンゾナイトと布部層は不整合関係にあり、不整合直上の基底礫岩からはウーライト石灰岩のブロックが含まれることが明らかとなった。従来、空知層群は深海底の堆積物と考えていたが、不整合とウーライト石灰岩の存在は、体積盆の一部が浅海、陸化していたことを示唆する。 Abstract: The upper Jurassic to lower Cretaceous Sorachi Group is Distributed along the western part of the Tokyo University Forests in Hokkaido, Japan. The Sorachi Group in this area consists mainly of mafic and intermediate igneous rocks, with subordinate volcanogenic sedimentary rocks. The group is divided into the Gokurakudaira Formation, Chikushidake Micromonzonite, Nunobe Formation, Ogurose Formation, and Rokugo Formation, in ascending order. An unconformity is found between the Chikushidake Micromonzonite and the Nunobe Formation, and the basal conglomerate on the unconformity contains oolite limestone blocks. These facts suggest that the Sorachi basin rose above the sea level, and...

  9. Geology and stratigraphy of forearc basin sediments in Hokkaido, Japan: Cretaceous environmental events on the north-west Pacific margin

    Takashima, Reishi; Kawabe, Fumihisa; Nishi, Hiroshi; Moriya, Kazuyoshi; Wani, Ryoji; Ando, Hisao
    Litho-, bio-, and chemostratigraphy of the Cretaceous forearc basin sediments exposed in Hokkaido, northern Japan allow a synthesis of the faunal, sedimentological, and environmental history of the north-west Pacific margin. Although the succession, named the Yezo Group, has yielded an abundant record of mid- to late Cretaceous invertebrates, monotonous lithologies of sandstone and mudstone, showing occasional lateral facies changes, have caused confusion regarding the lithostratigraphic nomenclature. Based on our wide areal mapping of the sequence, and analysis of litho- and biofacies, a new lithostratigraphic scheme for the Yezo Group is proposed. In ascending order, the scheme is as follows: the...

  10. First record of a Cretaceous cheilostome bryozoan from Hokkaido, Japan

    Ostrovsky, Andrew N.; Takashima, Reishi; Dick, Matthew H.; Grischenko, Andrei V.; Nishi, Hiroshi; Mawatari, Shunsuke F.
    A small collection of recrystallised, encrusting colonies of a single species from the Mikasa Formation (lower Middle Cenomanian), represents the first record of cheilostome (malacostegan or anascan) bryozoans from Hokkaido, Japan.

  11. Upper Albian to Lower Cenomanian biostratigraphy in the Oyubari area, Hokkaido, Japan: toward a Cretaceous biochronology for the North Pacific

    Kawabe, F.; Takashima, R.; Wani, R.; Nishi, H.; Moriyas, K.
    An integrated planktonic foraminifer and ammonoid biostratigraphy for the Oyubari area, Hokkaido, Japan, provides new insights into the late Albian to early Cenomanian biochronology of the North Pacific province. The following foraminifers extend Tethyan zonation to the Oyubari area: Biticinella breggiensis (lower Upper Albian), Rotalipora subticinensis - Rotalipora ticinensis (middle Upper Albian), Rotalipora appenninica (upper Upper Albian), and Rotalipora globotruncanoides (Lower Cenomanian) zones. Co-occurring age-indicative ammonoids such as Mortoniceras rostratum, Mariella bergeri, and Mantelliceras saxbii, are in accord with these foraminifer ages. The base of the Cenomanian stage in Hokkaido is recognized as the first occurrence of Rotalipora globotruncanoides, which...

  12. Late Jurassic–Early Cretaceous intra-arc sedimentation and volcanism linked to plate motion change in northern Japan

    The Sorachi Group, composed of Upper Jurassic ophiolite and Lower Cretaceous island-arc volcano-sedimentary cover, provides a record of Late Jurassic–Early Cretaceous sedimentation and volcanism in an island-arc setting off the eastern margin of the Asian continent. Stratigraphic changes in the nature and volume of the Sorachi Group volcanic and volcaniclastic rocks reveal four tectonic stages. These stages resulted from changes in the subduction direction of the Pacific oceanic plate. Stage I in the Late Jurassic was characterized by extensive submarine eruptions of tholeiitic basalt from the back-arc basin. Slab roll-back caused rifting and sea-floor spreading in the supra-subduction zone along...

  13. Directivity and apparent velocity of the coseismic ionospheric disturbances observed with a dense GPS array

    Heki, Kosuke; Ping, Jinsong
    Coseismic disturbances in ionosphere have been observed after recent thrust earthquakes off the Pacific coast of Japan, with a dense Global Positioning System array. Positive pulses in electron content, as large as several times 1015 electrons/m2 and as long as 4–5 min, emerge 10 min after earthquakes and propagate horizontally with apparent velocity of 1 km/s, close to the sound velocity at the ionospheric height. They may have been excited by coseismic uplifts of the sea surface initially as upward propagating compressive pulses of atmosphere, which were gradually refracted to propagate horizontally in ionosphere. The propagation has strong north–south asymmetry,...

  14. Explosion energy of the 2004 eruption of the Asama Volcano, central Japan, inferred from ionospheric disturbances

    Heki, Kosuke
    The Japanese dense array of Global Positioning System recorded ionospheric disturbances as changes in Total Electron Content ∼12 minutes after the September 1 2004 eruption of the Asama Volcano, Central Japan. The disturbance had a period of one and a quarter minutes and propagated as fast as ∼1.1 km/s, suggesting its origin as the acoustic wave generated by the explosion. By comparing the disturbance amplitudes with those by a surface mine blast with a known energy, the overall Asama explosion energy is inferred to be about 2 × 1014 J.

  15. The variations of stable carbon isotope ratio of land plant-derived n-alkanes in deep-sea sediments from the Bering Sea and the North Pacific Ocean during the last 250,000 years

    Ratnayake, Nalin Prasanna; Suzuki, Noriyuki; Okada, Makoto; Takagi, Miyuki
    Two piston cores, one located far from the continents (The North Pacific Ocean: ES core), and another located comparatively closer to the continents (The Bering Sea: BOW-8a core) were investigated to reconstruct environmental changes on source land areas. The results show significant contribution of terrestrial organic matter to sediments in both cores. The δ13C values of n-C27, n-C29, and n-C31 alkanes in sediments from the North Pacific ES core show significant glacial to interglacial variation whereas those from the Bering Sea core do not. Variations of δ13C values of land plant n-alkanes are related to the environmental or vegetational changes...

  16. Phosphatase and microbial activity with biochemical indicators in semi-permafrost active layer sediments over the past 10,000 years

    Takano, Yoshinori; Mori, Hideaki; Kaneko, Takeo; Ishikawa, Yoji; Marumo, Katsumi; Kobayashi, Kensei
    Core samples of boreal terrestrial sediments from depths of 0–300 cm at Rikubetsu, Hokkaido, Japan were analyzed for alkaline and acid phosphatase enzymatic activities. Enzymatic activities of alkaline phosphatase (ALP) and acid phosphatase (ACP) were greatest at the surface and decreased with depth; ALP and ACP activities were 25.5 and 22.0 nmol min(−1) g(−1), respectively, within the top 5 cm. These biological indicators were compared with measurements of microbial cell density and chemical indicators, including total organic C (TOC) and total hydrolyzed amino acids (THAA). The product–moment correlation coefficients (r) for ALP and ACP versus microbial cell density were 0.949...

  17. Emergence of the inflection point on racemization rate constants for d- and l-amino acids in the early stages of terrestrial diagenesis

    Takano, Yoshinori; Kobayashi, Kensei; Ishikawa, Yoji; Marumo, Katsumi
    The racemization rate constants of chiral amino acids such as asparagine and aspartate (Asx, kASX), glutamine and glutamate (Glx, kGLX) and alanine (Ala, kALA) were determined for terrestrial sediments from Rikubetsu, Hokkaido, Japan. The racemization rate constants, plotted in the form ln [(1 + d/l)/(1 − d/l)] versus sediment age, demonstrate that the initial rate constant was based on a fast racemization for l-form amino acids in the terrestrial sediment. The racemization reaction for labile organic matter on the surface could be markedly affected by the rapid hydrolysis: for example, the initial racemization rate constant kASX 1 was 1.1 ×...

  18. Coccolithophore assemblages and morphotypes of Emiliania huxleyi in the boundary zone between the cold Oyashio and warm Kuroshio currents off the coast of Japan

    Hagino, Kyoko; Okada, Hisatake; Matsuoka, Hiromi
    Living coccolithophore assemblages were studied off the Japanese coast in the boundary zone between the cold Oyashio and the warm Kuroshio Currents as well as in adjacent water masses. A total of 64 coccolithophore taxa were identified. Ten taxa that comprised more than 10% of at least one sample were designated major taxa. Morphological observations and morphometric measurements enabled us to sub-divide the Emiliania huxleyi into four morphotypes: Type A, Type B, Type B/C, and Type B/C-2. Based on the composition of major taxa and morphotypes of Emiliania huxleyi, four coccolithophore assemblages were recognized, corresponding to distinct water masses: Oyashio...

  19. Intra- and infra-specific morphological variation in selected coccolithophore species in the equatorial and subequatorial Pacific Ocean

    Hagino, Kyoko; Okada, Hisatake
    The ecological preferences of morphological groups within major coccolithophore taxa were studied in surface water samples from the equatorial and subequatorial Pacific Ocean. Emiliania huxleyi was subdivided into three morphological groups: Type A, Type C, and variety corona. The most probable factors limiting the occurrence of E. huxleyi Types A and C were high temperatures and low nutrient concentrations, respectively. E. huxleyi var. corona had an affinity for oligotrophic conditions. Calcidiscus leptoporus ssp. small was adapted to fertile waters. Umbilicosphaera foliosa and Umbilicosphaera sibogae preferred mesotrophic upwelling waters and stratified marginal waters surrounding the upwelling front, respectively. Among the three...

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