西南北海道渡島半島の新第三系層序と古地理  [in Japanese] Neogenestratigraphy and paleogeography of the Oshima Peninsula, southwest Hokkaido, Japan  [in Japanese]

西南北海道の新第三系を6期に区分し, 新しいF.T.年代測定値を加えて層序対比と各期の古地理図の作成を試みた。福山期(後期漸新世-前期中新世)は陸上での玄武岩質から流紋岩質の火山活動で特徴づけられる。訓縫期-大安在川期(中期中新世)から黒松内期(後期中新世-鮮新世)にかけては海進があり, かつ堆積盆ごとに分化しながら深海あるいは浅海の環境にあった。著しい沈降部では主に安山岩質の水中火山活動が活発であった。瀬棚期(更新世)は浅海の環境にあり, 陸化した地域では主に安山岩質な火山活動が活発化した。

Tertiary formations widely distributed in southwest Hokkaido are summarized into six stages in ascending order as follows. 1) Fukuyama and Yoshioka stages (Late Oligocene-Early Miocene): The subaerial volcanism of basalt to rhyolite took place in the western area of southwest Hokkaido from Late Oligocene to Early Miocene time. 2) Kunnui-Oanzaiga was tage (Middle Miocene): The first transgression in Middle Miocene time resulted in two types of sedimentary facies; the deep sedimentary facies with subaqueous volcanic rocks (Kunnui type) and the shallow sedimentary facies (Oanzaigawa type). 3) Yakumo stage (Middle Miocene): The sedimentary basin of this stage slowly subsided and enormously thick sands and shales with minor andesitic rocks were deposited in the Oshima Peninsula area. A violent andesitic-rhyolitic subaqueous volcanism took place in the Kameda Peninsula area. 4) Kuromatsunai stage (Late Miocene-Pliocene): The formations of this stage are composed mainly of tuffaceous mudstone and diatomite with acidic tuff layers intercalated. The subsidence in this stage was followed by faulting and volcanism with a NW-SE trend. 5) Setana stage (Pleistocene): The shallow-marine sedimentary facies of the Setana stage is composed of laminated coarse sandstones which unconformably covers the underlying Miocene and Pliocene formations. In the land area volcanic activities were vigorous during Early to Middle Pleistocene time.