著者

奥田 昌明 安田 喜憲 瀬戸口 烈司

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.38, no.4, pp.287-295, 1999-08-01

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ギリシャ南島部コパイ湖の最終氷期に多産するキク亜科化石花粉について詳細な研究を行った結果,おもに<i>Matricaria</i>型および<i>Centaurea</i>から構成されていることが明らかとなった.この組成は,トルコのアナトリア高原南西部から報告されている後氷期の花粉組成ときわめてよく似ている.このことは,トルコの高原地帯における完新世の植生が,ギリシャ南部海岸低地における最終氷期植生の相似型となりうる可能性を示している.

著者

近藤 錬三 佐瀬 隆

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.25, no.1, pp.31-63, 1986-05-31 (Released:2009-08-21)

参考文献数

246

被引用文献数

22 35

著者

米倉 伸之 辻 誠一郎 岡村 道雄

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.36, no.5, pp.283-286, 1997-12-01

参考文献数

4

被引用文献数

1

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The aims of the symposium &ldquo;Termination of Last Glaciation and the Formation and Development of Jomon culture in Japan&rdquo; are to clarify (1) what changes have occurred in natural environments in and around the Japanese Islands from the Last Glacial Maximum to the Postglacial periods, (2) what changes have occurred from Late Paleolithic culture to Jomon culture in terms of the relationship between natural and cultural environments, in paticular changes in coastal and land ecosystems and ways of human life, and (3) how and when the Jomon culture was established in terms of natural environmental changes.<br>The symposium consisted of three different parts: (1) Last Glacial Maximum (the age of upper Paleolithic culture, 20-15ka), (2) a transition period from Late Glacial to Postglacial (the age of formation of Jomon culture, 15-10ka), and (3) Postglacial period (the age of the development of Jomon culture, after 10ka). The topics were presented by three speakers for each part from the viewpoints of geology, paleoecology, pedology, and archeology.<br>The topics of presentations in the symposium are the following: Upper Paleolithic culture in Japan and East Asia (Masao Ambiru); Spatial distribution of the vegetation around the Last Glacial Maximum in Japan (Mutsuhiko Minaki); Paleoenvironmental changes of the Japan Sea since the Last Glacial period (Ryuji Tada); A land ecosystem in the transition to the Jomon age (Sei-ichiro Tsuji); The formation of Jomon culture in the Southern and Northern parts of Japanese Islands (Michio Okamura); Soil formation and the environmental change (Kan-ichi Sakagami); Development of Jomon villages (Yasuhiro Okada); Forest vegetation and utilization of wood during the Jomon period in Japan (Mitsuo Suzuki and Shuichi Noshiro), and Jomon agriculture: retrieval of evidence (Masakazu Yoshizaki). The discussions in the symposium have focused on the relationship between the changes in natural environments and ways of human life, in particular the change of land ecosystems and the utilization of natural resources.<br>The state of the art in studies of the natural environmental changes from the termination of the Last Glacial to the Postglacial and their relations to the regional development from the upper paleolithic culture to the Jomon culture in Japan are reviewed from various viewpoints, and future tasks of research are presented.

著者

岡村 道雄 中村 俊夫 辻 誠一郎 春成 秀爾 小野 昭 斉藤 文紀

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.40, no.6, pp.535-543, 2001-12-01

著者

岡村 道雄

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.36, no.5, pp.319-328, 1997-12-01

参考文献数

37

被引用文献数

1 7

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人類活動と自然環境の因果関係を研究するためには,地域的に両者の実像と変遷を捉えなければならない.特に,人類活動に大きな影響を与える因子に,気候と動植物相が考えられるが,それらの日本列島内での時空的な実態はほとんど明らかにされていない.ここでは,両者の関連が考察でき,自然環境と道具の組み合わせに地域性が認められる九州南部,東海東部から関東,中部・信濃川中流域,北海道を中心に分析してみた.晩氷期に南九州・四国南岸から南関東の太平洋沿岸部に,クリ・クルミ・ドングリ類が実る中間温帯林,豊かな縄文的な森が形成されはじめ,植物性食料の採取・加工に磨石・石皿・土器など,森に増殖しはじめたシカ・イノシシなどの狩猟に落とし穴や石鏃が用いられはじめた.一方,列島の北半は,完新世になっても旧石器時代的な寒冷気候が継続し,北アジアと同一歩調で細石刃が発達した.本州では少量の土器が用いられるが,木の葉形の石槍,打製石斧,有舌尖頭器を用いた狩猟を中心とした生業が続き,本州中部を境に北と南の縄文文化が成立した.

著者

石村 大輔 吉永 佑一 山田 圭太郎 原口 強 遠田 晋次

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.56, no.6, pp.265-270, 2017-12-01 (Released:2018-02-17)

参考文献数

23

被引用文献数

2

著者

五十嵐 八枝子 五十嵐 恒夫 大丸 裕武 山田 治 宮城 豊彦 松下 勝秀 平松 和彦

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.32, no.2, pp.89-105, 1993-05-31 (Released:2009-08-21)

参考文献数

38

被引用文献数

31 37

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北海道北部の剣淵盆地と中央部富良野盆地で14C年代の測定と花粉分析により約32,000年間の植生変遷史を復元した. 25,000~32,000yrs BPはエゾマツ/アカエゾマツを主とし, グイマツを混じえたタイガ, 16,000~25,000yrs BP (極相期) は現在のサハリン北部に見られるステップとグイマツ, ハイマツを主とする疎林 (北部) およびグイマツ, ハイマツを主とするタイガ (中央部)が発達した. 12,000~16,000yrs BPは北部でグイマツが衰え, エゾマツ/アカエゾマツとカバノキを主とする森林が発達した. 10,000~12,000yrs BPに著しい寒さの戻り (剣淵亜氷期) があり, グイマツは極相期の規模に回復した. 8,000~10,000yrs BPにグイマツは絶滅し, 8,000yrs BPにコナラ属が急増して現在の森林が形成された.

著者

西村 裕一 宮地 直道 吉田 真理夫 村田 泰輔 中川 光弘

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.39, no.5, pp.451-460, 2000-10-01 (Released:2009-08-21)

参考文献数

31

被引用文献数

11 10

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北海道東部の霧多布湿原において,湿原堆積物の掘削調査から泥炭層中に連続する層厚3cm以下の砂層を発見した.この砂層は,海側から内陸側に向かって層厚や粒径を減じ,比較的層厚の大きな地点では級化構造を呈する.また,乾燥化や塩分濃度の低下に伴って発生する珪藻化石を産出することから,この砂層を津波堆積物と認定した.砂層の下位には泥炭層を挾み,1739年の樽前a火山灰(Ta-a)と1694年の駒ヶ岳C2火山灰(Ko-c2)の2層の火山灰層が確認された.これらの火山灰層の年代をもとに泥炭の堆積速度を求めたところ,この砂層の年代はおよそ1810~50年代と推定された.1843年に,北海道東部の厚岸を中心に46名の犠牲者を出した北海道南東岸沖地震津波の歴史記録があり,この津波の前後に規模の大きな津波が霧多布湿原一帯に押し寄せた記録はないことから,本砂層は1843年の津波によりもたらされた堆積物と考えられる.

著者

大森 博雄 柳町 治

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.30, no.1, pp.1-18, 1991-02-28 (Released:2009-08-21)

参考文献数

24

被引用文献数

1 1

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The subalpine zones on the mountains south of the Tohoku mountains in the Japanese Islands are normally occupied by coniferous forests dominated by Abies mariesii, A. veitchii, Picea jezoensis var. hondoensis and Tsuga diversifolia. But there are many mountains where the subalpine coniferous forest does not exist; the thermometrical subalpine zones on such mountains are replaced by subalpine and/or montane deciduous broad-leaved forests. Especially in the Tohoku mountains, the subalpine zone without A. mariesii forest is called the “pseudo-alpine zone”, where Quercus scrub usually dominates. The origin of the pseudo-alpine zone is discussed here based on the thermal conditions of subalpine main tree species and the rise in temperature during the Hypsithermal climax phase.The thermometrical zone for A. mariesii is divided into four ranges as shown in Fig. 5-b. The mountains whose peaks are thermometrically in zones B and C can be regarded as mountains where A. mariesii is alternatively indigenous or not indigenous under the present thermal conditions. On the mountains whose peaks are in zone A, A. mariesii is expected to be indigenous. Thus, the mountains in zone A but without A. mariesii forest are called the “A. mariesii-lacking mountains” and are examined here.For the “A. mariesii-lacking mountains”, the thermal conditions at their peaks were out of zone A and into zones B and/or C during the Hypsithermal climax phase, when the mean summer temperature rose to be 2.5°C higher than that at present in Japan. During the high-temperature period of the Hypsithermal, the habitat of A. mariesii was pushed over the mountain peak due to the upward migration of vegetation zones. Thus, the principal cause of the pseudo-alpine zone is the ‘pushing-out effect’ caused by the rise of temperature. The origin of the subalpine zones without subalpine coniferous forest in West Japan is also considered to be the same process as the pseudo-alpine zone in the Tohoku mountains. The lacking of a tree species on a mountain depends on a process in which the thermal conditions suitable for the species disappeared from the mountain during a period in the history of climatic changes and, since the event, the thermal habitat of the species has been isolated from the surrounding mountains with forests of the same species. The present features of distribution of the subalpine tree species which grow under cold climatic conditions on high mountain areas in Japan have been affected by the small changes (2 or 3°C) in temperature during the Holocene, reflecting the topographical mosaic built up by many small mountain blocks and inter-lowlands.

著者

貝塚 爽平

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.23, no.2, pp.55-70_1, 1984-07-31 (Released:2009-08-21)

参考文献数

98

被引用文献数

19 18

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Landforms in and around the South Fossa Magna, which are shown in Figs. 2 and 3, and the history of their growth during the late Cenozoic are described. The pattern of the tectonic landforms and the history of their growth are explained by a tectonic model shown in Fig. 5.The South Fossa Magna consists mainly of strongly folded and thrust Neogene and Quaternary strata along the subduction and collision zone between the overriding Eurasian plate (or the Eurasian and North American plates) and the subducting Philippine Sea plate. The collision occurred on the north of the Izu Peninsula during the past 1-0.5 Ma. The characteristic landform in the folded zone is flights of elongated domes or ridges, called outer ridges.There are three areas with different topography and tectonic history in central Honshu to the north of the plate boundary; they are, from west to east, 1) the Akaishi Mts-Tokai lowland and offshore area, 2) the Kanto Mts-Misaka Mts-Tanzawa Mts area, and 3) the Kanto Plain-Miura-Boso Hills and their offshore area. To the south of the plate boundary, there are three different belts in the northeastern part of the Philippine Sea (PHS) plate; they are, from west to east, i) the Shikoku Basin, ii) the inner volcanic arc (Izu Inner Bar), and iii) the outer non-volcanic arc (Izu Outer Bar) of the Izu-Bonin arc.The PHS plate moved to the north after the spreading of the Shikoku Basin (30-15 Ma BP), and different physical property and somewhat different speed of movement of the three belts gave different tectonic features to the three areas in central Honshu as is shown in Fig. 5 (A). Then the PHS plate collided with Honshu on the northern side of the Izu Peninsula, and changed the direction of movement to the northwest in 1-0.5 Ma BP. Quaternary uplift of the Akaishi, Tenshu, Misaka, and Tanzawa Mts thus started, while the processes of making the outer ridges ceased under a rather extensional stress field in the Miura-Boso Hills and their offshore area of southern Kanto as shown in Fig. 5 (B). Collision between the northeast Japan arc (on the North American plate) and the Southwest Japan arc (on the Eurasian plate) may have occurred along the Fossa Magna in the Quaternary Period.

著者

中島 礼 伊藤 光弘 兼子 尚知 樽 創 利光 誠一 中澤 努 磯部 一洋

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.43, no.3, pp.225-230, 2004-06-01

参考文献数

12

被引用文献数

1

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茨城県つくば市東部を流れる花室川の中流域から,<i>Palaeoloxodon naumanni</i> (Makiyama)の臼歯が発見された.産出層準は,最上部更新統である桜川段丘堆積物に相当する緩斜面堆積物で,約2.7万年前より新しい年代を示す.歯種は左上顎第3大臼歯であり,歯冠長は331mm,咬板数は1/2・22・1/2と,これまでに報告された臼歯の中でも大型であり,特に咬板数は最大であることがわかった.この標本の産出は,<i>P.naumanni</i>の時代的な形態変異を明らかにする上で重要である.

著者

藤根 久 小坂 和夫

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.36, no.1, pp.55-62, 1997-02-28 (Released:2009-08-21)

参考文献数

42

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生駒山地西麓地域(東大阪市河内地域)から産出する縄文時代後期および晩期の土器の中には,その胎土が暗褐色~茶褐色を呈し,角閃石類を多量に含むという特徴を有する土器群があることが知られている.これらの特徴を有する土器は,“河内の土器”と一般的に呼称されており,他地域の土器とはもちろん,この地域のほかの土器とも容易に識別される.これらの土器について,土器薄片を作成し,偏光顕微鏡下において観察と記載とを行った.その結果,(1)これらの胎土中の粒子の大きさ分布は5μmから250μmの範囲で,破砕物が一般的に示すフラクタル性(スケーリング則)を有すること,(2)粘土の質・量とも断層内物質の一般的特徴を有すること,(3)粘土は一般的に用いられていたものとは異なり,接着性が非常に高い特異なものであることが明らかになった.さらに,鉱物・岩石片からなる粒子には,破片状の尖った外形を呈するものが多く,断層岩に特徴的な粒内微小断層や微角礫状組織あるいはカタクラサイト状組織を呈するものもあり,顕著な不連続的波動消光や双晶面のたわみ・キングバンドや機械的双晶という変形岩・断層岩を特徴付ける組織が多いこと,が明らかになった.以上のような土器胎土の特徴から,その材料として断層内物質が用いられた可能性がきわめて大きいと考えられ,胎土材料としてほかの材料を考えることは困難である.その産地としては,岩石学的・地質学的特徴から生駒山地西縁を南北に走る生駒断層の破砕帯が最も可能性が高いものとしてあげられる.

著者

工藤 雄一郎 小林 謙一 山本 直人 吉田 淳 中村 俊夫

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.47, no.6, pp.409-423, 2008-12-01 (Released:2012-03-26)

参考文献数

48

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石川県御経塚遺跡から出土した縄文時代後・晩期の土器付着物と漆の14C年代,炭素・窒素安定同位体比,C/N比の測定を行い,土器で煮炊きされた内容物と各土器型式の年代学的位置づけについて検討した.その結果,後期の内面付着炭化物は,動物資源を煮炊きしたものが炭化して残ったものと考えられ,このうちのいくつかは海洋リザーバー効果の影響を受けている可能性を指摘した.晩期の土器付着物の14C年代は,周辺地域の研究成果と対比しても整合的であった.そこで,晩期の土器付着物の14C年代をIntCal04で較正し,晩期中葉の中屋式,晩期後葉の下野式および長竹式の較正年代を提示した.晩期最終末の長竹式の年代は,北陸地域における環状木柱列の形成時期とも関係することが明らかとなり,これは縄文時代から弥生時代への移行期の問題を検討する上で,きわめて重要な成果である.

著者

藤井 理行

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.37, no.3, pp.181-188, 1998-07-31

参考文献数

20

被引用文献数

2 1

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グリーンランド氷床のコアの安定酸素同位体組成の解析により,Dansgaard-Ocschgerサイクルと呼ばれる氷期における24ものinterstadials(亜間氷期)が明らかとなった.interstadialsは,数十年間で5~7℃の急激な温暖化とその後500~2,000年の緩やかな寒冷化で特徴づけられる気温変動である.また,Dansgaard-Oeschgerサイクルを束ねたBondサイクルと呼ばれる気温変動は,ローレンタイド氷床から北大西洋への氷山群の流出(ハインリッヒイベント)後に急激な温暖化で始まることが,海底コアとの対比で明らかとなった.本論では,氷期における北大西洋深層水(NADW)の消長による海洋での熱塩循環の変動が,地球規模での気候を支配してきたことを示すとともに,気候システムには2つの安定なモードがあることを指摘する.さらに,現在進行中の温暖化に伴う降水量の増加により,北大西洋海域の塩分濃度が低下し,熱塩循環が止まり,現在とは別の気候モード(寒冷化)が引き起こされる可能性を紹介する.

著者

新井 房夫 小林 国夫 直良 信夫

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.10, no.4, pp.191-201, 1971-12-25 (Released:2009-08-21)

参考文献数

36

被引用文献数

1 1

著者

松下 勝

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.27, no.4, pp.273-278, 1989-03-31 (Released:2009-08-21)

参考文献数

38

被引用文献数

1 1

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In carrying out archaeological excavations and studies on remains of rice paddy fields, many problems cannot be solved without the help of the methods and techniques of natural science. Several such problems of considerable importance are detecting the sites, analyzing for what purpose they were used, clarifying the system for their utilization, establishing their chronology, estimating the harvest, determining the factors allowing for the existence of the rice paddy fields, their surrounding environment, and the effects of their cultivation on the natural environment.Observation of the soil section combined with pollen analysis has been successfully used in detecting the horizon of the site. Investigation of macro-remains of culture plants and other weeds contributed to recognition of the difference between rice paddy fields and dry agricultural fields, or to determining whether a rice field was dry or wet. Conventionally, in estimating a rice harvest, not only archaeological, but also bibliographical or agricultural methods have been applied. Analysis of plant opal, developed in recent years, reveals itself as a method superior to these conventional ones. To analyze the factors which made possible the establishment of the site, the methods mentioned above-for example, reconstruction of paleo-vegetation based on the pollen analysis-have been used. Recently, a method which could be referred to as micro-scale topographyenvironment analysis has been used successfully in investigating the relationship between rice field cultivation and topography and water supply.The number of branches of archaeology in which methods of natural science can be used successfully will increase also in the future. We should be aware, however, that analysis of archaeological material seldom yields any positive result unless the archaeologist, in consultation with the natural scientist, has a clear aim in utilizing such analyses. Establishing a data base to accumulate the archaeological data yielded by methods of natural science is necessary; such a data base may be useful for many disciplines in archaeological studies. More important, however, is the careful observation of sites in situ to establish the correct chronology of multi-layered archaeological sites and to estimate the time gap between succeeding layers, because the factors controlling the duration of cultivation of a rice field are multidimensional.

著者

森脇 広 岩田 修二

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.31, no.4, pp.229-241, 1992-10-31 (Released:2009-08-21)

参考文献数

48

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最終氷期のアイスランドは, その主要部を一続きの氷床に覆われていたが, 周辺部の山岳地帯は周辺部が薄いアイスドームからなっていた. 晩氷期末の最高位旧汀線の高度分布はこの氷河分布に対応し, 島の主要部は一続きの広い曲隆域となり, 北西地域に小曲隆部がある. 晩氷期以後, 古ドリアス期と新ドリアス期の再拡大期 (ほぼ同規模) があった. その後氷河は大きく縮小したが, ネオグレシエーション以後拡大し, 現在のようになった. 氷河融解にともなう隆起は完新世初期には終了した. 後期更新世末から完新世初期にかけての隆起量は最大150mに及ぶ. 現在の海岸地域は完新世中期以降は全体としては沈降している.

著者

吉川 虎雄

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.7, no.4, pp.157-170, 1968-12-20 (Released:2009-08-21)

参考文献数

37

被引用文献数

9 4

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The Pacific coast of Southwest Japan has been attacked by violent earthquakes accompanied by remarkable crustal deformation at intervals of 100 to 150 years in the historical period. At the most recent great earthquake in 1946, promontories protruding south into the Pacific Ocean were upheaved by about one meter, being tilted northwards, and inland mountainous regions were subsided. The mode of recent crustal deformation, including seismic one, of Shikoku has been revealed with precise levellings, as shown in Figs. 1-3.In the southern part of Shikoku runs a hinge line of the recent crustal deformation, which was subsided at the seismic time and upheaved in the inter-seismic periods. The coastal areas south of the hinge line were tilted southwards in the inter-seismic periods and remarkably northwards at the seismic time, while the mountainous region north of the line was quite reversely deformed.In the vicinity of Muroto Promontory, the southeastern tip of Shikoku, a characteristic process of post-seismic crustal deformation was clarified with precise levellings carried out seven times for six years after the great earthquake in 1946 (Okada et al., 1953). Immediately after the earthquake, Muroto Promontory was rapidly tilted southwards, and then the rate of southward tilting exponentially decreased to become as constant as in the pre-seismic period. The post-seismic crustal deformation (Fig. 3) is nearly reverse to the seismic one (Fig. 2) and is different in its mode from the pre-seismic one (Fig. 1), while similar minor features are found in their mode. It is, therefore, inferred that the post-seismic crustal deformation was chiefly caused by seismic after-effect and the pre-seismic crustal deformation resulted from secular tectonic movement and decelerated seismic after-effect.From this inference secular crustal deformation of Shikoku was tentatively estimated, by subtracting the post-seismic vertical displacement from the triplicated pre-seismic one. Although there is no definite reason for triplicating the latter, the estimated secular crustal deformation (Fig. 6) is nearly concordant with the patterns of geomorphological and geological structure of the mountains, and is negatively correlated with Bouguer's anomalies of gravity (Geogr. Surv. Inst., 1966).Resultant crustal deformation of Shikoku in the seismic and inter-seismic periods was also obtained from results of precise levellings (Fig. 7), assuming that great earthquakes accompanying crustal deformation of similar mode have occurred at intervals of about 120 years. Coastal terraces on the south coast descend northward and their heights have a positive correlation with the resultant deformation (Fig. 9). Topographic features of various types caused by subsidence are found along the hinge line, which is inferred to have been subsided as a result of the seismic and inter-seismic crustal deformation. Heights of the mountains north of the hinge line show positive correlations with the resultant deformation, except in the central part of the western Shikoku Mountains, and coefficients of regression are larger in higher mountains than in lower ones (Figs. 10 and 11). In the coastal areas south of the hinge line, however, correlation between heights of the mountains and the resultant deformation are negative (Figs. 9 and 11). This means that the mountains have been upheaved by tectonic movement of similar mode to the recent crustal deformation including seismic one, which probably dates from before the formation of coastal terraces and at least after the evolution of the lower mountains.A quite similar relation between the recent crustal deformation and the geomorphic features is also found in Kii Peninsula, east of Shikoku.

著者

中西 利典 木村 治夫 松山 尚典 ホン ワン 堀川 義之 越後 智雄 北田 奈緒子 竹村 恵二

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.58, no.2, pp.163-173, 2019-04-01 (Released:2019-06-04)

参考文献数

29

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中央構造線活断層系の西端に位置する別府湾は,およそ5Maから沈降場にある.その南縁の府内断層は同堆積盆を構成する主要な正断層である.その活動性を評価するために,断層を挟んで掘削された7本のボーリングコア試料を用いて,堆積相解析,珪藻化石の群集組成解析,合計17試料の陸源植物片と4試料の海生炭酸塩の放射性炭素年代測定を実施した.それらの解析結果を基にして,デルタフロント相,デルタプレーン相,人工盛土相を認定した.これらの堆積構造と変形構造は地中レーダ探査によって可視化された.これらの結果,デルタプレーン相の最上部の泥層の堆積年代と珪藻化石群集を基にして800~400calBPの最新活動を認定した.デルタフロント相の泥層の上下変位量を基にして2,100calBP頃の活動も認定した.これらからおよそ1,700年の再来間隔が計算できる.

著者

岡口 雅子

出版者

Japan Association for Quaternary Research

雑誌

第四紀研究 (ISSN:04182642)

巻号頁・発行日

vol.15, no.3, pp.97-108, 1976-10-30 (Released:2009-08-21)

参考文献数

22

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The Oita district is a standard area for the Cenozoic stratigraphy in West Japan. Above all the Tsurusaki hills is regarded as the most important area including the type sections of three formations. Main parts of the Takio, the Higashiwasada and the Tsurusaki formations are distributed respectively in the central to north area, in the south and north extremity. They are overlain by the higher terrace sediments. In the south of the hill, the gravels of the Higashiwasada formation, the Takio formation and the higher terrace sediments are developed in intricate pattern and their stratigraphic relation is misleading suggesting that some of these are possibly contemporaneous. While the known index fossil from the formation is only Stegodon orientalis from the basal part of the Tsurusaki formation. Accordingly the supposed ages of the Takio and Higashiwasada formation based on an indirect correlation is not accurate. Therefore it is important to clarify their ages.For settling these problems, the fission track age determination of the accessory zircon from pyroclastic rocks from above mentioned formations were done after a systematic field survey.In norder to observe fission tracks easily and correctly, the etching procedure was examined and the condition was finally settled as following; the etchant was 2:1 mixture of 48%HF and 98% H2SO4 and etching is carried out under pressure at 250°CThe Shikido pyroclastic rock member of the Higashiwasada formation and the Hada pyroclastic rock member of the Takio formation were selected for examination. The age of the Shikido and the Hada pyroclastic rock members are (6.52±1.34)×106 year and (1.44±0.28)×106 year, respectively.The age of the Shikido pyroclastic rock member is comparable with some volcanic rocks in Central Kyushu, for example biotite andesite in Kitatakaki District, Nagasaki Prefecture (5.7m.y.B.P.), biotite hornblende rhyolite in Hirado City (5.8m.y.B.P.), etc. Considering sporadical distribution, in Central Kyushu of volcanic rocks with similar lithology to those of the Higashiwasada formation, it must be concluded that the volcanic activity of this age is more extensive than has been supposed.The Hada pyroclastic rock member is correlative with the Meisei tuff bed at MaO horizon of the Osaka group. Comparing the relative position of the Hada pyroclastic rock member and the Stegodon orientalis horizon in the Oita group with the relative position of the Meisei tuff bed and the Stegodon orientalis horizon in the Osaka group, the writer conclude that the Takio formation correspons to the lower and middle parts of the Osaka group.