著者

早津 賢二

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.14, no.1, pp.1-13, 1975-04-30 (Released:2009-08-21)

参考文献数

24

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The Myoko volcano, one of the stratovolcanoes in the northern part of the Fossa Magna, Central Japan, has the complicated history (Table 1).The last activity of the Myoko volcano is called the IV stage, and is divided into precaldera, caldera, and central cone substages. The strata formed during this stage are collectively called the Myokosan group which consists of lavas, pyroclastic flow deposits, pyroclastic fall deposits, volcanic mud flow deposits, and lake deposits. They are described in detail and their stratigraphic relations are tabulated in Table 2 and Fig. 4.The rocks of the essential eruptives are basalt, pyroxene andesite and hornblende andesite. They change from basalt to pyroxene andesite and hornblende andesite keeping step with the eruptive order. Quantitatively, the hornblende andesite is predominant.

著者

松岡 数充

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.17, no.3, pp.165-170, 1978-11-30 (Released:2009-08-21)

参考文献数

13

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The Nanmatsu Formation was newly described from the western part of the Tsugeno district, Nara Prefecture. It consists-of sands, silts and peaty muds with a characteristic volcanic ash layer. Abundant macro and micro-fossils of plants revealed were described. The radiocarbon dating of the formation using a piece of wood identified as Picea indicates the age of 28, 100±800 y. B. P.The plant fossil assemblage is characterized by an abundant occurrence of leaves, twigs, wood and pollen of such coniferous trees as Abies, Picea, Tsuga and Pinus including subgen. Haploxylon. Macro and micro fossils of deciduous broad-leaved trees are scarcely occurred. There is an evidence that the Nanmatsu Formation deposited during the Würm Glacial Age, and it appears to state that a coniferous forest mainly composed of Abies veitchii and/or A. homolepis, Picea polita, Tsuga diversifolia and Pinus subgen. Haploxylon pentaphylla might be occupied around the area of the Tsugeno district.

著者

西田 史朗

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.30, no.4, pp.239-250, 1991-10-30 (Released:2009-08-21)

参考文献数

15

被引用文献数

1

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Vertical variations of volcanic glass major element composition were examined on two representative volcanic ash layers of the Pleistocene Osaka Group, namely the Pink and Azuki Volcanic Ash Layers. Both layers are widely distributed in the Kinki district, well exposed in its surrounding hilly area, and are most reliable marker beds in their stratigraphy.The Pink Volcanic Ash Layer lies on the widespread Marine Clay 1 (Ma 1) horizon and is estimated at ca. 0.92 Ma in FT-age. The Azuki Volcanic Ash Layer is interbedded also in the transgressive Marine Clay 3 (Ma 3) and is measured at ca. 0.87 Ma in FT-age. At both sides of the Azuki we can recognize drastic climatic and vegitational changes in the fossil evidence.In this study major element composition of volcanic glass shards were analyzed with an energy-dispersive X-ray micro-spectrometry by grain-by-grain method. Analytical results were processed statistically and offered for further discussion.On the chemical stratigraphy, the Pink Volcanic Ash Layer shows a stable compositional succession in major elements through a whole layer, in spite of its clear lithological facies change, especially in grain size distribution and matrix clay color.The Azuki Volcanic Ash Layer shows two types of sedimentary facies. One is a direct fall and water-laid-type deposit, and the other is a water-transported-type deposit. Binocular observation shows that Azuki volcanic glasses are composed of two type of glass, colorless and colored. Color variation in the latter ranges from light brown to deep brown and sometimes opaque black. In this study black and opaque glass shards are rejected and restricted in transparent glass only.In Azuki Volcanic Ash glass, major element composition is stable in the colorless layer and changes drastically in the colored glass, about 10cm above the base. In addition, the colored Azuki Volcanic Ash Layer shows a gradual change in chemical composition within the layer, and chemical composition shows little difference in the two types of glass because of admixture and sorting during transportation.

著者

公文 富士夫 河合 小百合 井内 美郎

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.42, no.1, pp.13-26, 2003-02-01 (Released:2009-08-21)

参考文献数

45

被引用文献数

19 24

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1988年に野尻湖湖底から採取されたオールコア試料の上部について,30~50年間隔の精度で有機炭素(TOC)・全窒素(TN)の測定と花粉分析を行った.4点の14C年代測定,鬼界アカホヤ(K-Ah)および姶良Tn(AT)の指標火山灰年代に基づいて推定した堆積年代と,TOC・TNおよび花粉の分析結果に基づくと,遅くとも14C年代で1.4~1.5万年前より前には落葉広葉樹花粉の増加で示されるような温暖化が始まり,以後,「寒の戻り」を伴いながら約1万年前まで温暖化が進行した.約1.3万年(較正年代1.5万年前)前後には,「寒の戻り」を示す亜寒帯針葉樹花粉の明瞭な増加が認められる.約1,2万年前(較正年代1.4万年前)には,広葉樹花粉の急増と針葉樹花粉の激減があり,同時に全有機炭素・窒素量の激増も認められ,短期間のうちに急激に温暖化が進行したと推定される.なお,14C年代で約1.45万年前にも微弱な広葉樹花粉の減少が認められる.これらの気候変動のパターンは,北大西洋地域の気候イベント(新旧ドリアス期など)とよく似ているが,本稿における編年に基づけば,北大西洋地域よりもそれぞれ2,000~3,000年ほど古いようにみえる.較正年代で約1.3万年前と9千年前においても,軽微な気候変動が認められ,そのうちの後者はボレアル期に対比できる.

著者

安藤 一男

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.25, no.3, pp.165-176, 1986-12-31 (Released:2009-08-21)

参考文献数

19

被引用文献数

6 8

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Minuma Lowland is an erosional valley that lies in the Oomiya Upland, Saitama Prefecture. The author has investigated the stratigraphy of the Holocene deposit filling the erosional valley. The surface deposit is about 6.5 meters thick and is composed of peat and gray clay. This is underlain by a sand bed over 6-15 meters thick. Moreover, the author has investigated the Holocene Paleoenvironments and the highest sea level based on the diatom assemblages contained in their deposits in the Minuma Lowland. Diatom assemblages from this area showed that the highest level of the sea attained was at least +3.9-+4.1 meters above sea level. The highest stage of the sea level is probably younger than about 5950-5540y.B.P.

著者

百原 新 斎木 健一 奥田 昌明

出版者

日本第四紀学会

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.45, no.3, pp.211-216, 2006 (Released:2007-07-27)

参考文献数

18

被引用文献数

7 9

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千葉県袖ケ浦市吉野田の更新統下総層群清川層 (MIS7.3) から, ナウマンゾウやシカ, カメ類化石とともに11分類群の大型植物化石が取り上げられた. 大型植物化石群は, サルスベリ属, ハリモミ近似種, ブナ, フジを含み, いずれも印象化石だった. このうち, サルスベリ属はヤクシマサルスベリ近似の化石種に同定された. 吉野田の当時の気候は, シマサルスベリの北限の温量指数102℃月前後の気温条件と推定された.