Bulletin of the Geological Survey of Japan

The North Kitakami Belt in Northeast Japan mainly comprises accretionary complexes formed during the Jurassic to earliest Cretaceous. The accretionary complex of the North Kitakami Belt is less studied compared to the age-equivalent accretionary complexes in Southwest Japan. Here, we provide additional data on the accretionary complex formerly classified as the Otori Unit, distributed in the northeastern part of the North Kitakami Belt in the upper reaches of the Akka River in Iwate Prefecture. Based on detailed field mapping, we clarified that the Otori Unit is composed of the structurally lower coherent facies of chert and siliceous mudstone (Okoshizawa Subunit) and the structurally upper mixed facies of mudstone, sandstone, chert and minor basaltic rocks (Osakamoto Subunit). Manganese nodules from siliceous mudstone within the Okoshizawa Subunit yielded radiolarians indicating the Bathonian (upper Middle Jurassic). Detrital zircon grains from sandstone in the Osakamoto Subunit has a youngest age of ~170 Ma (YC1σ: 171.8 ± 2.4 Ma; YSG: 170.9 ± 3.8 Ma). Based on the radiolarian and detrital zircon ages, the accretionary age of the Otori Unit is estimated as the Bathonian. Our new data were also considered to discuss the correlation between the North Kitakami Belt and the Southern Chichibu Belt in Southwest Japan. The Otori Unit corresponds to the Ohirayama Unit of the Southern Chichibu Belt in structural position, and the two units are similar in being a mixed facies and have overlapping accretionary age. However, the Otori Unit lacks limestone and has a considerably younger age for siliceous mudstone, suggesting that the two units may not be strictly correlative.

Shun MUTO

Tsuyoshi ITO

Masafumi MURAYAMA

BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN

Geology and accretionary age of the Otori Unit, North Kitakami Belt

北北上带大鸟单元的地质与增生时代

Yukio YANAGISAWA

Hisao ANDO

Sora KUSHIBIKI

Stratigraphy and diatoms of the Neogene Taga and Hitachi groups in the Hanareyama district, Kuji Town, Hitachi City, Ibaraki Prefecture, Japan

日本茨城县日立市久慈町鼻山地区中新世多贺组和日立组的地层与硅藻

Jun HOSOI

Diatom biochronology and U–Pb age of the Miocene strata in the Satomi area along eastern margin of the Tanakura sedimentary basin, Japan

日本田仓沉积盆地东缘佐藤地区中新世地层的硅藻生物年代学与U-Pb年龄

海洋地質図の作成を目的として，GB21-1航海はトカラ列島南西沖を中心にマルチチャンネル反射法音波探査を行った．高密度な測線間隔の反射断面をもとに，音響層序及び地下構造をまとめた．火山フロント西方では不整合面を基準にOT1層からOT4層の4層を区分した．火山フロント西方で認められた断層は，OT1層に変位を生じさせた正断層とOT3層に累積性のある変位を生じさせた正断層を識別した．OT1層に変位を生じさせた正断層は西横当海丘東方で北北東–南南西走向に分布する．OT3層に累積性のある変位を生じさせた断層は火山フロント西方に広く分布し，沖縄トラフ東縁部で北東–南西走向を，宝島南西沖で東北東–西南西走向を呈する．OT3層に累積性のある変位を生じさせた断層は，OT2層堆積後に北部沖縄トラフ背弧拡大に起因する北西–南東方向の引張応力によって形成されていると考えられる．火山フロント東方では，音響的な層相の違い及び断層に伴って生じたと考えられる不整合面をもとにして地層をTK1層からTK4層の4層に区分した．火山フロント東方に分布する断層は，TK4層に累積性のある変位を与えた正断層とTK3層及びTK4層に同様の変位を与えた正断層に識別された．TK4層に累積性のある変位を与えた正断層は，調査海域南端である奄美舟状海盆の北縁にて東西走向で認められた．TK3層及びTK4層に同様の変位を与えた正断層は，宝島東方に西北西–東南東走向で分布する．調査海域で追跡可能であった断層の特徴は火山フロントの東西で異なることが明らかになった．今後，音響層序にもとづいた断層の特徴と堆積層の年代分析を組み合わせることにより，琉球弧北部のテクトニクスに関する議論の発展が期待される．

Saki ISHINO

Ayanori MISAWA

Jun ARIMOTO

Takahiko INOUE

Seismic survey of GB21- 1 Cruise off southwest Tokara Islands

西南吐噶喇群岛外海GB21-1航次地震调查

トカラ列島南部海域において実施した海底地質調査航海GB21-1では，61地点で表層採泥，2地点で柱状試料採泥を実施した．おおむね水深800 m以上の平坦な海底には泥質堆積物が分布し，多くの地点で強い生物擾乱を受けている．コア試料分析によれば，生物擾乱の影響は少なくとも海底下約2 m程度まで見られる．砂質堆積物や礫，露頭の分布は，必ずしも浅い水深には限定されない．こうした底質分布は島嶼部に加えて海底下の堆積物供給源となりうる海底火山の存在に規制されていると思われる．宝島周辺で多く見られるリップルなどのベッドフォーム，生物遺骸の局所的な濃集，露頭や礫質堆積物の分布は，本海域で蛇行する黒潮の強い影響を示唆する．諏訪之瀬島南西方では，海底表面にリップルを呈する火山灰質砂層の下位に泥質堆積層が存在し，その粒径コントラストや粒子組成から，諏訪之瀬島など近傍の陸地から，例えば斜面崩壊などを起源としてイベント的に堆積した可能性がある．

Yoshiaki SUZUKI

Takuya ITAKI

Hajime KATAYAMA

Naotomo KANEKO

Makoto YAMASAKI

Yuki TOKUDA

Asuka SENTOKU

Submarine sediment distribution and its controlling factors around the Takarajima Island and the Suwanosejima Island

宝岛和西表岛周边海底沉积物分布及其控制因素

Toshiki OHTAKI

Simple estimation of an S-wave velocity profile by adding one three-componentgeophone to a P-wave reflection survey line

通过在P波反射测量线上增加一个三分量检波器来简单估算S波速度剖面

Satoru TAKAHASHI

Seasonal Variation of Transportation of Manila (Asari) Clam Larvae in Hiroshima Bay

广岛湾马尼拉蛤仔幼虫运输的季节性变化

Toshio KAWAMURA

Takayuki UCHINO

ジルコンU–Pb 年代測定による南部北上帯の石炭紀火山活動期の制約

锆石U-Pb年代测定对南部北上带石炭纪火山活动期的限制

Publication Information	Publisher: National Institute of Advanced Industrial Science and Technology (AIST)，Publishing cycle: ，Journal Type: journal，Open Access Journals: No
Basic data	Year of publication: 2010，Proportion of original research papers: ，Self Citation Rate:， Gold OA Rate:

Bulletin of the Geological Survey of Japan

Journal Citation Format

A journal article with 1 author

A journal article with 2 authors

A journal article with 3 authors

A journal article with 5 or more authors

Books Citation Format

Thesis Citation Format

Web sites Citation Format

Patent Citation Format

Staying up late manually editing references? ivySCI automatically matches journals and helps you generate references with a single click.

Share Submission Experience

Geology and accretionary age of the Otori Unit, North Kitakami Belt

Stratigraphy and diatoms of the Neogene Taga and Hitachi groups in the Hanareyama district, Kuji Town, Hitachi City, Ibaraki Prefecture, Japan

Diatom biochronology and U–Pb age of the Miocene strata in the Satomi area along eastern margin of the Tanakura sedimentary basin, Japan

Seismic survey of GB21- 1 Cruise off southwest Tokara Islands

Submarine sediment distribution and its controlling factors around the Takarajima Island and the Suwanosejima Island

Stratigraphy and diatoms of the Neogene Taga and Hitachi groups in the Hanareyama district, Kuji Town, Hitachi City, Ibaraki Prefecture, Japan

Diatom biochronology and U–Pb age of the Miocene strata in the Satomi area along eastern margin of the Tanakura sedimentary basin, Japan

Simple estimation of an S-wave velocity profile by adding one three-componentgeophone to a P-wave reflection survey line

Seasonal Variation of Transportation of Manila (Asari) Clam Larvae in Hiroshima Bay

ジルコンU–Pb 年代測定による南部北上帯の石炭紀火山活動期の制約