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Title: 北海道夕張-芦別地域に分布する空知層群・蝦夷層群の層序と堆積環境
Other Titles: Stratigraphy and sedimentary environments of the Sorachi and Yezo Groups in the Yubari-Ashibetsu area, Hokkaido, Japan
Authors: 高嶋, 礼詩1 Browse this author
吉田, 武義2 Browse this author
西, 弘嗣3 Browse this author
Authors(alt): Takashima, Reishi1
Yoshida, Takeyoshi2
Nishi, Hiroshi3
Keywords: Jurassic
Sorachi Group
Yezo Group
Issue Date: 15-Jun-2001
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: 107
Issue: 6
Start Page: 359
End Page: 378
Abstract: 北海道の夕張-芦別地域に分布する最上部ジュラ系~下部白亜紀の空知層群は, ピクライトおよび安山岩質からデイサイト質の火山砕屑岩類を主体とし, 大陸地殻起源のアルコース質砂岩を伴う.これに整合に累重する白亜系蝦夷層群は, 陸源の砂岩・泥岩からなり, 石灰岩ブロックを含むオリストストロームと珪長質凝灰質砂岩層の2つの特徴的な堆積物を挟在する.空知層群下部は, 従来, 無斑晶質の玄武岩が卓越するとされてきたが, 本地域では全てピクライトで, それに安山岩質とデイサイト質の火山砕屑岩, アルコース質砂岩を挟在する.また, 空知層群は深海底の堆積物とされていたが, ウーライト石灰岩を伴うことから堆積場の一部は浅海域であったことが示唆される.
The Upper Mesozoic Sorachi and Yezo Groups are widely distributed in the Yubari-Ashibetsu region, located in the axial zone of central Hokkaido, the northernmost island of Japan. The Sorachi Group in this area consists mainly of volcanic rocks and volcaniclastic turbiditic rocks, and is divided into the Gokurakudaira, Ashibetsugawa, Nakatengu and Shirikishimanaigawa Formations in ascending order. The Gokurakudaira Formation constitutes mostly picrites, accompanied by intercalation of dacitic-andesitic volcaniclastic rocks and arkosic terrigenous turbiditic sandstones derived from the East Asian Continent. The Ashibetsugawa Formation is composed of medium-bedded red mudstone with several andesitic volcanic sandstone beds. The other two formations are characterized by andesitic volcaniclastic rocks. The rocks of the Nakatengu Formation are thick breccia beds and very thin-bedded mudstones, while those of the Shirikishimanaigawa Formation are thick- to medium- bedded sandstones, mudstones and tuff. The Yezo Group conformably overlying the Sorachi Group comprises alternating beds of terrigenous turbiditic sandstone and hemipelagic mudstone, presumably resulted from the erosion of the uplifted Jurassic accretionary prisms (Oshima Belt) located in southwestern Hokkaido. The two stratigraphic marker units of olistostrome unit containing "Orbitolina Limestone" blocks (the Upper Aptian Kirigishiyama Olisto- strome Member) and felsic tuffaceous unit (the Upper Albian Maruyama Formation), are recognized in the Yezo Group. Based on the biostrati-graphic study using radiolarians and planktonic foraminifers, the Sorachi Group and the lower part of the Yezo Group range in age from Tithonian to early Albian. Many previous works have been considered that the Sorachi Group consisted of basaltic rocks and cherts. However, we found intercalation of thick sedimentary sequence composed of arkosic sandstones within the basaltic rocks in the investigated area. This suggest that the basaltic eruptions, in part, occurred in an adjacent area close to the Asian continent. Moreover, some volcaniclastic rocks of the Sorachi Group also contain many ooids including angular andesite fragments. The occurrence of these rocks also indicates shallow marine environment on the volcanic mound.
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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