No.123 研究課題 / Project
多摩丘陵内の段丘堆積物の珪藻化石群集とその堆積環境Fossil diatoms and their sedimentary environments in terrace deposits of Tama Hills| 学術研究 Academic Research |
No.123 |
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| 代表研究者 Principal Investigator |
大西 一博 Kazuhiro Onishi |
| 所属（採択当時） Affiliation |
都立大学理学部助手 Tokyo Metropolitan University |
| 研究内容要約 Research Summary |
本調査地域の多摩丘陵は、第四紀中・後期を通して隆起傾向にあったため段丘群の発連がよい。これらの段丘はこの期間に形成された時代の異なる数種類の段丘に区分される。そしてそれらは火山灰層序学的検討やその層相変化・貝化石などの特徴から、一般に氷河時代と呼ばれる更新世における世界的な気侯変動とそれに伴う海水準変動により形成されたものと推定されてきた。 しかしその堆稜環境の変遷についての微化石を用いた検討は、今までほとんどなされていない。これはわが国における微化石研究者の少なさにもよるが、これらの段丘堆積物層における層序が極めて難しいことにもよる。 最近、これら段丘堆積物層にはさまれる火山灰層の研究から、本地域の中、後期更新世における地史について新しい考え方が提示された。 そこでこの新しい層序に基づき、本研究では現在盛んな宅地開発による多数の人口的露頭を調査し、それらより選定された段丘堆積物層の露頭から経時的な試料を採取し、その中の珪藻化石、植物珪酸体、古鞭毛虫類（Archaeomonads）などの珪質微化石の分析を行ない、堆積環境の復原を試みる。 All through the Middle and Late Quaternary Period, many upheavals took place in the Tama Hills, the areas surveyed in this study, and therefore there are well developed terraces in the Hills. These terraces can be classified into several types, based on the periods when they were developed. According to tephrostratigraphic (volcanic ash layer stratigraphy) analysis and the characteristics of facies changes and fossil seashells, it was generally believed that these terraces were formed as a result of global climate changes during the Pleistocene Epoch, commonly known as the Ice Age, and of the following eustatic change of sea level. However, so far virtually no microfossil-based research has been conducted to understand changes in sedimentary environments. This is because there are only a few microfossil researchers in Japan , and, more importantly, because the stratigraphy of terrace sedimentary layers is extremely complex. Thanks to stratigraphic research for in-between volcanic ash layers, a new theory was recently proposed for the geological history of the Middle and Late Quaternary Period. On the basis of this new theory, this research was performed as follows: we surveyed artificial outcrops that had emerged in large numbers as a result of residential development; we collected chronological samples at some specific outcrops of terrace sedimentary layers, and then analyzed siliceous microfossils, such as fossils diatoms, plant-derived silica bodies, and archaeomonads, in order to reconstruct the sedimentary environments. |
| 共同研究者 Collaborators |
鹿島 薫、高野繁昭 |
| 研究全文 Full Text |
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