| Project/Area Number |
01540642
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Stratigraphy/Paleontology
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| Research Institution | HOKKAIDO UNIVERSITY |
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Principal Investigator |
KOIZUMI Itaru HOKKAIDO UNIV., DEPART.SCI.PROFESSOR, 理学部, 助手 (20029721)
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| Co-Investigator(Kenkyū-buntansha) |
FUKUSAWA Hitoshi HOKKAIDO UNIV., DEPART.SCI.ASSISTANT, 理学部, 助手 (80208933)
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| Project Period (FY) |
1989 – 1990
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| Project Status |
Completed (Fiscal Year 1990)
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| Budget Amount *help |
¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 1990: ¥200,000 (Direct Cost: ¥200,000)
Fiscal Year 1989: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Keywords | ANIAI-TYPE FLORAS / DAIJIMA-TYPE FLORAS / DIATOM ASSEMBLAGES / JAPAN SEA / DIATOMACEOUS SEDIMENT / YAMATO RISE / BACK-ARC SPREDING / FRESH-WATER LAKE / 阿仁合型植物群 / 台島型植物群 / 混合型植物群 / 珪藻化石 / リフト / 阿仁合型化石植物群 / 台島型化石植物群 / 淡水生珪藻化石群集 / 汽水生珪藻化石群集 / 淡水湖 / グリ-ンタフ変動 |
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| Research Abstract |
THE SEDIMENTS INCLUDING FRESH-WATER DIATOMS ACCOMPANIED WITH THE ANIAI-TYPE FLORAS ARE OLDER THAN 20MA, AND ANOTHER ONES ACCOMPANIED WITH THE DAIJIMA-TYPE FLORAS FROM 18 TO 16MA ARE ESTIMATED TO BE OF A BRACKISH-WATER ORIGIN.THESE EARLY MIOCENE SEDIMENTS ARE RECOGNIZED IN AREAS ALONG THE PERIPHERY OF THE JAPAN SEA AND IN THE SAMPLES FROM THE YAMATO RISE.THE DIATOM ASSEMBLAGES ACCOMPANIED WITH THE ANIAI-TYPE FLORAS CHARACTERISTICALLY CONSIST OF PREDOMINANT MELOSIRA DISTANS, MELOSIRA GRANULATA, MELOSIRA ISLANDICA, AND ASSOCIATED FORMS OF FRESH-WATER DIATOMS.AN ADMIXTURE OF BRACKISH AND MARINE DIATOMS IS NOT OBSERVED.THE DIATOM ASSEMBLAGES ACCOMPANIED WITH THE DAIJIMA-TYPE FLORAS, ON THE OTHER HAND, ARE CHARACTERIZED BY THE MIXING OF SEA-WATER DIATOM ACTINOCYCLUS OCTONARIUS AND A FRESH-WATER DIATOM ASSOCIATION PREDOMINATING MELOSIRA DISTANS, MELOSIRA GRANULATA, AND MELOSIRA ISLANDICA.THIS TYPE OF ADMIXTURED DIATOM ASSOCIATION IS ALSO RECOGNIZED IN THE SAMPLES FROM THE YAMATO RISE.A LARGE FRESH-WATER LAKE HAD BEEN EXISTED BETWEEN THE ASIAN CONTINENT AND JAPAN ISLANDS DURING THE PERIOD OLDER THAN 20MA BEFORE THE BACK-ARC SPREADING OF THE JAPAN SEA.ENVIRONMENTAL CHANGES OF THE FRESH-WATER LAKE BY INVADED SEA-WATER CAN BE TRACED SEQUENTIALLY AT SEVERAL SITES IN THE JAPAN SEA AND ALSO IN THE PERIPHERY OF THE JAPAN SEA.THE DIATOMACEOUS SEDIMENTS OF THE JAPAN SEA COAST ORIGINATE IN A SEDIMENTARY ENVIRONMENT CHARACTERIZED BY SUBSIDING, SILLED SMALL BASINS DURING THE ROTATION OF THE JAPANESE ISLANDS AND THE RISING EUSTATIC SEA LEVEL DURING THE CLIMATIC OPTIMUM IN THE EARLY MIDDLE MIOCENE.THE DEPOSITION OF PURE DIATOMACEOUS SEDIMENTS IS MARKED BY THE FIRST APPEARANCE OF THE COLD-WATER DIATOM DENTICULOPSIS PRAEDIMORPHA.IT IS CONSIDERED THAT MOST OF THE YOUNGER DIATOMACEOUS SEDIMENTS RESULTED FROM THE CONVERGENCE OF COLD AND WARM CURRENTS OVER THE CONTINENTAL SLOPE.
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