著者

横山 芳春 安藤 寿男 大井 信三 山田 美隆

出版者

The Sedimentological Society of Japan

雑誌

堆積学研究 (ISSN:1342310X)

巻号頁・発行日

vol.54, no.54, pp.9-20, 2001-12-25 (Released:2010-05-27)

参考文献数

25

被引用文献数

2

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茨城県石岡-鉾田地域における下総層群“見和層”を対象に詳細な堆積相解析, 侵食面・火山灰鍵層の追跡を行った結果, 2回の堆積サイクルの存在が確認できた. 下位のサイクル1は西部の大規模な谷地形を充填する開析谷埋積システムと, これを覆って調査地域全域に分布する外浜-海浜システムの堆積物からなる. サイクル2ではバリアー島・潟システムの堆積物が特徴的に発達し西部で厚く保存されているが, 東部では外浜-海浜システムの堆積物がこれを覆って分布している. 常総層は主に河川システムの堆積物からなるが, 調査地域東部では下部に海成層が認められた. シーケンス層序学的解釈を行った結果, サイクル1にはシーケンス境界 (SB1), 内湾ラビンメント面 (BRS1), 波浪ラビンメント面 (WRS1) の3枚の侵食面が認められ, サイクル2にはSB2, BRS2, WRS2, SB3の4枚の侵食面が認められた. それぞれの堆積サイクルにはTST, HSTが認められ, 2回の相対海水準変動に伴う堆積シーケンスを構成していることが判明した.

著者

横山 芳春 大井 信三 中里 裕臣 安藤 寿男

出版者

The Sedimentological Society of Japan

雑誌

堆積学研究 (ISSN:1342310X)

巻号頁・発行日

vol.55, no.55, pp.17-28, 2002-11-20 (Released:2010-05-27)

参考文献数

34

被引用文献数

3

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茨城県東茨城台地西部において下総層群“見和層”及び涸沼段丘礫層を対象に堆積相解析, 火山灰鍵層の対比および地形学的考察を行った結果, 以下のことが判明した. 本地域の層序は,“見和層”サイクル1,“見和層”サイクル2, 涸沼段丘礫層に区分することができる.“見和層”サイクル1は泥質なエスチュアリー成堆積物から形成され, 古涸沼川が形成した開析谷とその埋積物からなる.“見和層”サイクル2は, 上位段丘面を構成し. 東茨城台地西部で内湾成の堆積相が, 東部で外洋成の堆積相が発達することから, 潟・バリアー島システムによって形成された可能性が高い. 潟・バリアー島システムを反映した堆積相分布は, 離水後の微地形や水系発達に大きな影響を与えた. すなわち, バリアー島内湾側では潟の泥質堆積物が保存され, 広く浅い谷が形成された. さらに, 泥質堆積物は水系分布を制約し, 扇状の分岐や大きく屈曲する水系が形成された. 一方, 外洋側では浜堤平野を形成した浜堤列群が保存され, 北東から南西方向の浅い谷の凹地と微高地の凸地が発達したものと解釈される.

著者

山口 晴幸 横山 芳春

出版者

Japan Society of Civil Engineers

雑誌

地球環境シンポジウム講演論文集 (ISSN:18848419)

巻号頁・発行日

vol.6, pp.269-278, 1998-07-09 (Released:2011-06-27)

参考文献数

5

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In this report, the present authors discussed on the coastal pollution by foreign drifted garbages. The field investigations were carried out at the points of 224 in Japanese seashore-lines. The type and classification of foreign drifted garbages were investigated. It was points out from the results of field investigations that the coastal pollution by foreign drifted garbages was very important environmental problem in Japan.

著者

大井 信三 横山 芳春

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.117, no.Supplement, pp.S103-S120, 2011-09-01 (Released:2013-02-20)

参考文献数

49

被引用文献数

2 2

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茨城県中・南部の常陸台地を構成する下総層群は,これまで房総半島の模式層序との対比が確立されておらず,地域内でも研究者によって様々な見解があり,異論が多かった.そこで新たに見いだされたテフラを広域に追跡することでテフラ層序を組み立てて,それを基準として堆積相解析やシーケンス層序学的解析を行った.その結果,下総層群を藪層,上泉層,清川層,横田層,木下層,常総層の6層を区分した.さらに,最終間氷期の堆積物である木下層に2つの堆積サイクルを認め,剣尺(けんじゃく)部層,行方(なめかた)部層を新たに設定した.本巡検では常陸台地における下総層群の各構成層について,案内者らの見解を紹介し,模式層序との対応を解説,議論する.さらに,テフラと堆積相の分布から推定される,木下層の堆積過程について概説する.特に堆積物供給量の違いを背景として,涸沼(ひぬま)を境界として南北で異なる堆積システムの時空変化について,常陸台地を縦断して比較を行う.

著者

横山 芳春 安藤 寿男 橋本 聡子

出版者

日本古生物学会

雑誌

化石 (ISSN:00229202)

巻号頁・発行日

no.76, pp.32-45, 2004-09-22

被引用文献数

1

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Large oyster shell beds are contained in incised-valley fill deposits of the Cycle 1 of the Miwa Formation, Shimosa Group, Lake Kasumigaura area, Ibaraki Prefecture . This paper describes taphonomic processes of large oyster shell beds well exposed in three localities . Six shell bed types can be recognized on the basis of their lithology, sedimentary facies, mode of fossil occurrence and associated fossils : 1) autochthonous aggregated, 2) autochthonous scattered, 3) parautochthonous aggregated, 4) cross-bedded aggregated, 5) crossbedded scattered and 6) shell-fragment aggregated types. The large oyster shell bed higher than 5 m and wider than 30 m at east Hama (Loc. 1) is characterized by type 1 with two layers of type 3 five to 20 cm thick that seem to have formed by sudden storm events. The second shell bed at west Hama (Loc. 2) shows two mounds 3 m high and or wider than 7-10 m composed of type 1 and covered by massive muddy sediments. This means that the oyster banks were buried under estuary mud. The last example at Sakihama (Loc.3) is the largest oyster shell bed in this area with height of 5m and width of 70m. It can be divided into three unit bounded by two erosional surfaces. The unit I is composed mainly of type 1 representing in situ oyster reefs, and subordinately of 3 formed by reworking through tidal current. The unit II composed of types 4 and 5 forms a shallow channelfilled structure that seems to have been formed as a tidal channel. The overlying unit III above a flat erosional surface mostly consists of type 6. Reworked oyster shell fragments might have concentrated intermittently and condensed through muddy sediment bypassing within tidal flat to embayment.

著者

大井 信三 横山 芳春 西連地 信男 安藤 寿男

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.119, no.7, pp.488-505, 2013-07-15 (Released:2013-11-02)

参考文献数

47

被引用文献数

1 2

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茨城県常陸台地を構成する下総層群の層序区分については,房総半島との対比が確立されておらず,研究者の意見の一致をみていない.本論では特に層序的な問題が多い木下層について,テフラの岩相と岩石記載,屈折率や火山ガラスの主成分化学組成を分析し,それらに基づいて給源火山域および鹿島沖海底コア(MD01-2421)中のテフラと広域対比を試みた.対比および対比の可能性のあるテフラは,ArPはNk-Yt,OiPはNk-Nm,ObはTAu-9,KtPと鹿島沖海底コアTephra20(1)である.広域対比の結果,ArP,TAu-9がMIS 5e前期,OiPがMIS 5e最盛期,KtPがMIS 5d初期に降灰したとみなされる.これによって,木下層剣尺部層の堆積年代がMIS 6~MIS 5e,行方部層がMIS 5d初期であると解釈される.

著者

横山 芳春 中村 裕昭

出版者

The Geological Society of Japan

雑誌

日本地質学会学術大会講演要旨 (ISSN:13483935)

巻号頁・発行日

pp.291, 2012 (Released:2013-03-26)

著者

横山 芳春 大久保 拓郎

出版者

The Geological Society of Japan

雑誌

日本地質学会学術大会講演要旨 (ISSN:13483935)

巻号頁・発行日

pp.295, 2014 (Released:2015-03-16)

著者

木村 由莉 横山 芳春 平野 弘道

出版者

日本古生物学会

雑誌

化石 (ISSN:00229202)

巻号頁・発行日

vol.90, pp.5-15, 2011-09-30 (Released:2017-10-03)

参考文献数

26

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Molluscan fossils in storm-generated shell beds are commonly transported and damaged. Here we report a case study on assessing mollusc shell transport from original habitats to lower shoreface storm deposits. Fossil assemblages recovered from eight storm-generated shell beds in the Pliocene Dainichi Formation, Kakegawa Group, Japan, were examined. We assessed temporal changes in the relative frequency of three ecological categories (mode of life of bivalves, substrate preference, and habitat depth), using available information on modern molluscan species. The studied stratigraphic section was subdivided into two distinct units based on taxonomic compositions and the ecological categories. The lower unit (D-1, D-2, D-2') is characterized by rocky-bottom dwellers such as Area arabica, Cardita leana, Chama sp., Lima vulgaris, Collisella spp., and Siliquaria cumingii. The gravelbottom dweller Arcopsis symmetrica is more common in the lower unit. The upper unit (D-3 to D-7) can be distinguished from the lower one by a decrease in deposit feeders that are better able to escape sudden burial than suspension feeders. In this unit, suspension feeders that generally inhabit quiescent environments increase in the place of the deposit feeders. The results indicate the followings: (1) the storm-generated shell beds in the study section represent indigenous fossil assemblages; (2) thin and flat bivalves (e.g., "Macoma" spp. and Saccella spp.) exclusively deposited on the laminar surface (D-2') were more or less transported, whereas gastropods accumulated in lag deposits (D-2) of hummocky cross-stratified beds were residues after a storm event and its attendant winnowing of fine sediments; (3) paleontological evidence obtained from the lower unit indicates the existence of a rocky coast during the time when the Dainichi Formation began to deposit in the study area (Dainichi, Fukuroi City); and (4) the changes in the ecological categories from the lower to the upper unit are compatible with the upward-deepening sedimentary sequence recorded in the Dainichi Formation.

著者

横山 芳春 安藤 寿男 橋本 聡子

出版者

日本古生物学会

雑誌

化石 (ISSN:00229202)

巻号頁・発行日

vol.76, pp.32-45, 2004

参考文献数

52

被引用文献数

1

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Large oyster shell beds are contained in incised-valley fill deposits of the Cycle 1 of the Miwa Formation, Shimosa Group, Lake Kasumigaura area, Ibaraki Prefecture . This paper describes taphonomic processes of large oyster shell beds well exposed in three localities . Six shell bed types can be recognized on the basis of their lithology, sedimentary facies, mode of fossil occurrence and associated fossils : 1) autochthonous aggregated, 2) autochthonous scattered, 3) parautochthonous aggregated, 4) cross-bedded aggregated, 5) crossbedded scattered and 6) shell-fragment aggregated types. The large oyster shell bed higher than 5 m and wider than 30 m at east Hama (Loc. 1) is characterized by type 1 with two layers of type 3 five to 20 cm thick that seem to have formed by sudden storm events. The second shell bed at west Hama (Loc. 2) shows two mounds 3 m high and or wider than 7-10 m composed of type 1 and covered by massive muddy sediments. This means that the oyster banks were buried under estuary mud. The last example at Sakihama (Loc.3) is the largest oyster shell bed in this area with height of 5m and width of 70m. It can be divided into three unit bounded by two erosional surfaces. The unit I is composed mainly of type 1 representing in situ oyster reefs, and subordinately of 3 formed by reworking through tidal current. The unit II composed of types 4 and 5 forms a shallow channelfilled structure that seems to have been formed as a tidal channel. The overlying unit III above a flat erosional surface mostly consists of type 6. Reworked oyster shell fragments might have concentrated intermittently and condensed through muddy sediment bypassing within tidal flat to embayment.

著者

横山 芳春 七山 太 安藤 寿男 大塚 一広

出版者

日本古生物学会

雑誌

化石 (ISSN:00229202)

巻号頁・発行日

vol.74, pp.7-17, 2003-09-20 (Released:2017-10-03)

参考文献数

30

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伊予灘海域で採取された下灘コアの層相および軟体動物化石群を検討した結果は, 以下の4つにまとめられる.1.下灘コアの層相およびこれに含まれる軟体動物化石の解析結果に基づき, DU-A〜Eの5つの堆積ユニットを識別した.このうち最下位のDU-Aを除く上位4ユニットには, 海成粘土層が発達する.2.下灘コア中に認められる軟体動物化石群は, 松島(1984)の区分した感潮域, 干潟, 内湾停滞域, 内湾泥底および沿岸砂泥底の5つの群集の構成種からなる.さらに土石流堆積物には複数の群集構成種が混合した化石群が認められる.3.堆積ユニットごとに見ると, DU-Bには感潮域化石群, DU-Cには感潮域化石群および干潟化石群が認められ, 縄文海進に伴って感潮域〜干潟が拡大したことを反映しているものと解釈される.DU-Dは内湾停滞域化石群が認められ, 水塊の交換に乏しい内湾の停滞水域下で堆積したものと考えられる.DU-Eには内湾泥底〜沿岸砂泥底化石群が認められ, 下位より潮通しの良い内湾環境下で堆積したものであろう.4.下灘沖において海水が侵入し, エスチュアリー〜干潟環境が成立, 感潮域群集の構成種が出現した年代は約12000〜11000年前以前であろう.約10000年前には急激な相対海水準上昇が生じたため, 感潮域群集および干潟群集が内湾停滞域群集へ急速に群集変化したのであろう.これは地震イベントに伴って, 下灘沖の地溝帯が急激に沈降したことによる可能性が高い.約10000年〜8000年前には, 内湾停滞域群集が発達する閉鎖的な内湾停滞域が形成され, 周囲の河川から流入した細粒物質が大きな堆積速度をもって沈積していた.約8000年前以降は内湾泥底〜沿岸砂泥底群集が生息する潮通しの良い内湾環境へと変化したが, これは地溝帯の埋積と同時に瀬戸内海の成立に伴ったものである可能性が示唆される.

著者

横山 芳春 安藤 寿男 橋本 聡子

出版者

日本古生物学会

雑誌

化石 (ISSN:00229202)

巻号頁・発行日

vol.76, pp.32-45, 2004-09-22 (Released:2017-10-03)

被引用文献数

1

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Large oyster shell beds are contained in incised-valley fill deposits of the Cycle 1 of the Miwa Formation, Shimosa Group, Lake Kasumigaura area, Ibaraki Prefecture . This paper describes taphonomic processes of large oyster shell beds well exposed in three localities . Six shell bed types can be recognized on the basis of their lithology, sedimentary facies, mode of fossil occurrence and associated fossils : 1) autochthonous aggregated, 2) autochthonous scattered, 3) parautochthonous aggregated, 4) cross-bedded aggregated, 5) crossbedded scattered and 6) shell-fragment aggregated types. The large oyster shell bed higher than 5 m and wider than 30 m at east Hama (Loc. 1) is characterized by type 1 with two layers of type 3 five to 20 cm thick that seem to have formed by sudden storm events. The second shell bed at west Hama (Loc. 2) shows two mounds 3 m high and or wider than 7-10 m composed of type 1 and covered by massive muddy sediments. This means that the oyster banks were buried under estuary mud. The last example at Sakihama (Loc.3) is the largest oyster shell bed in this area with height of 5m and width of 70m. It can be divided into three unit bounded by two erosional surfaces. The unit I is composed mainly of type 1 representing in situ oyster reefs, and subordinately of 3 formed by reworking through tidal current. The unit II composed of types 4 and 5 forms a shallow channelfilled structure that seems to have been formed as a tidal channel. The overlying unit III above a flat erosional surface mostly consists of type 6. Reworked oyster shell fragments might have concentrated intermittently and condensed through muddy sediment bypassing within tidal flat to embayment.

著者

横山 芳春 山辺 雅志 加藤 未希 大久保 拓郎

出版者

The Geological Society of Japan

雑誌

日本地質学会学術大会講演要旨 (ISSN:13483935)

巻号頁・発行日

pp.282, 2015 (Released:2016-03-31)

著者

横山 芳春 木村 由莉

出版者

一般社団法人 日本地質学会

雑誌

日本地質学会学術大会講演要旨 第112年学術大会(2005京都) (ISSN:13483935)

巻号頁・発行日

pp.104, 2005-09-10 (Released:2017-08-21)

著者

山口 晴幸 横山 芳春

出版者

Japan Society of Civil Engineers

雑誌

地球環境シンポジウム講演論文集 (ISSN:18848419)

巻号頁・発行日

vol.6, pp.269-278, 1998

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In this report, the present authors discussed on the coastal pollution by foreign drifted garbages. The field investigations were carried out at the points of 224 in Japanese seashore-lines. The type and classification of foreign drifted garbages were investigated. It was points out from the results of field investigations that the coastal pollution by foreign drifted garbages was very important environmental problem in Japan.

著者

上田 庸平 ジェンキンズ ロバート G 安藤 寿男 横山 芳春

出版者

日本古生物学会

雑誌

化石 (ISSN:00229202)

巻号頁・発行日

vol.78, pp.47-58, 2005

参考文献数

26

被引用文献数

3

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Various-sized and -shaped calcareous concretions occur abundantly in the Lower Miocene Kokozura Formation of the Takaku Group which crops out on the Izura coast and its nearby north, Kita-Ibaraki City, north of Ibaraki Prefecture. The Kokozura Formation is mainly composed of intensely bioturbated, very fine-grained muddy sandstone, which may have been deposited on the outer shelf of the Joban forearc basin. The calcareous concretions are divided into the following six types on the basis of their shapes, sizes and modes of occurrence : Type I (large-sized concretions with undulatory surface, 1 to 6m in diameter), Type II (smaller, less than a few decimeters in diameter, and irregular-shaped concretions closely associated with Type I), Type III (pipe-shaped hollow concretions, a few decimeters in diameter and less than 2m in length), Type IV (sheet to lenticular concretions, 10 to 20cm in thickness and a few meters in lateral length), Type V (burrow-fill sand concretions concentrated and connected to each other in very fine-grained sandstone) which grades upward into Type VI (concreted sandstone bed, 2 to 3m in thickness, including abundant burrows). In the lower part of the outcrop, the Types I and II are dominant and commonly associated with Type III, whereas the uppermost part consists of Types V and VI which developed into a huge concreted bed, 2 to 3m thick, over 50m wide and 100m long. ^<13>C-depleted carbon isotopic compositions (-20.9 to -29.2‰ vs PDB) of Types I and II suggests that these concretions were formed under the influence of methane seepage. Molluscan assemblages dominated by Lucinoma acutilineatum are associated with the Type I, II, and III concretions. Most of L. acutileatum shells keep their life position. The mode of fossil occurrence indicates that L. acutileatum formed a chemosynthetic community and used methane seepage through chemosynthetic bacteria for their energy source.