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THE STUDY ON PALEOGEOGRAPHIC CHANGE OF THE JAPAN SEA BASED ON THE DIATOM ASSEMBLAGES AND SEDIMENTARY FACIES ACCOMPLISHED THE OPENING OF THE JAPAN SEA

基于硅藻组合和沉积相的日本海古地理变化研究实现了日本海的开放

基本信息

批准号：
01540642
负责人：
KOIZUMI Itaru
金额：
$ 0.9万
依托单位：
HOKKAIDO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

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.

沉积物包括淡水硅藻，其年龄大于20 Ma，18 ~ 16 Ma时与大岛型植物群伴生的硅藻化石，估计为半咸水成因，这些早中新世沉积物在日本海周边地区和大和隆起的样品中均有发现。模式植物群主要由远直链藻、颗粒直链藻、海岛直链藻和相关的淡水硅藻组成。没有观察到半咸水硅藻和海洋硅藻的混合物。另一方面，特征是海水硅藻八角放线菌和淡水硅藻组合优势种远直链藻，颗粒直链藻，和Melosiraislandica。这种类型的混合硅藻协会也被确认在样品中的大和上升。一个大的新鲜-日本海弧前20 Ma以前在亚洲大陆与日本岛之间就存在着淡水湖.海水入侵对淡水湖环境的影响在日本海和日本海周边的几个地点可以连续追踪到水。日本海沿岸的硅藻沉积物起源于一种沉积环境，中中新世早期日本列岛旋转期间的小型冰碛盆地和气候最佳期的海平面上升。水硅藻DENTICULOPSIS PRAEDIMORPHA.据认为，大多数较年轻的硅藻沉积物是由大陆斜坡上的冷、暖流汇合而成的。