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Title: 中蝦夷地変の再検討と北海道の白亜紀テクトニクス
Other Titles: Re-evaluation of the intra-Yezo disturbance and the Cretaceous tectonics in Hokkaido, Japan
Authors: 高嶋, 礼詩1 Browse this author
西, 弘嗣2 Browse this author
Authors(alt): Takashima, Reishi1
Nishi, Hiroshi2
Keywords: Hokkaido
Yezo Group
intra-Yezo disturbance
basal conglomerate
felsic volcanism
Issue Date: 15-Oct-1999
Publisher: 日本地質学会
Journal Title: 地質學雜誌
Journal Title(alt): Journal of the Geological Society of Japan
Volume: 105
Issue: 10
Start Page: 711
End Page: 728
Abstract: 白亜系蝦夷層群の下部と中部の境界(L/M境界)は不整合をもって定義され, この不整合を形成した変動は中蝦夷地変と呼ばれている.中蝦夷地変の時期や特徴を明らかにするため, 北海道中軸部に沿った添牛内, 大夕張-芦別, 金山西部, 金山南部, 双珠別, 日高およびイドンナップの7地域でL/M境界の"基底礫岩層"の岩相・堆積相・地質年代を再検討した.その結果, "中部蝦夷層群の基底礫岩層"とされていた岩相は, 西列に関しては蝦夷層群中部の丸山層最下部の土石流堆積物に対比され, 東列に関しては蝦夷層群下部シューパロ川層中部のオリストストローム層に相当し, いずれも基底礫岩とはいえない.したがって, 従来の中蝦夷地変において想定された不整合を形成する隆起帯は, 中期白亜紀には存在しなかった可能性が高い.しかしながら, 蝦夷層群の下部~中部にかけてはテクトニックな事件を示唆する堆積物が2層準(オリストストローム, 珪長質凝灰質砂岩層)に存在し, 中蝦夷地変にかわる事件として注目される.
Many previous works on the Central Hokkaido support a tectonic model that exposure of Kamuikotan metamorphic belt occurred in the middle Cretaceous, and that the Yezo sedimentary basin was divided into the western and eastern terranes by the movement. The recognition of this event named as "the intra-Yezo disturbance" is based mainly on the exsitence of unconformity where basal conglomerates of "the Middle Yezo Group" (the middle part of Yezo Group) overlie alternating beds and limestones of "the Lower Yezo Group" (the lower part of Yezo Group).On the basis of lithology, sedimentary facies and microfossil biostratigraphy in both basal conglo-merate beds and the underlying strata, conglomerates and breccias distributed in the Soeushinai and Oyubari-Ashibetsu areas of the western terrane of the Yezo Group are recognized as debris flow deposits associated with felsic tuff beds which are correlated with the late Albian Maruyama Formation, the middle part of the Yezo Group. In the western Kanayama, southern Kanayama, Soshubetsu, Hidaka and Idonnappu areas of the eastern terrane, basal conglomerates reported by the previous workers are olistostromes or redeposited conglo-merates which belong to the lower part of the Yezo Group and are assigned to the late Aptian. Hence, coglomerate beds in previous works can be classified into the Aptian olistostromes and the late Albian debris flow deposits associated with tuff beds. These two deposits are distributed widely in both eastern and western terranes of the Yezo Group. These observations suggest that conglomerates assignable to "the intra-Yezo disturbance" are not typical basal conglomerates, and the uplifted model of Kamikotan ridge needs to be reviced. Instead, the extensive distributions of olistostromes and tuff beds in the Central Hokkaido indicate two mid-Cretaceous tectonic events which are huge submarine sliding in the late Aptian, and the following large-scale felsic volcanism in the late Albian.
Type: article
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 高嶋 礼詩

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