北海道中央北部の新第三系の層序と古環境  [in Japanese] Stratigraphic and paleoenvironmental study of the Neogene formations in northern Central Hokkaido, Japan  [in Japanese]

北海道北部からサハリンにかけての日本海沿岸沿いには, 海成の新第三系が広く分布している。この論文では, 石狩炭田西縁から天北にかけての9地域に分布する新第三系の対比を行い, それらを下位から次の7層準に区分した。1) 曲渕・袋地層準, 2) 羽幌・三毛別層準, 3) 築別・鬼志別層準, 4) 増幌・古丹別層準, 5) 稚内層準, 6) 声問・遠別層準, 7) 勇知・更別層準。その資料を基礎に, 築別・鬼志別層堆積時(16 Ma), 増幌・古丹別層堆積時(15 Ma), 稚内層堆積時(10 Ma), 勇知・更別層堆積時(4 Ma)の古地理図を描いた。この地域は, 中期中新世以降, 日本海堆積盆の北部を占め, 北海道中軸部の急激な上昇にともなう東方からの堆積物の供給によって埋積され, 浅海化して行った。

Marine Neogene sediments are widely distributed along the Japan Sea coast from northern Hokkaido to Sakhalin. We constructed the four paleogeographic maps of the northern Central Hokkaido from late Early Miocene toPleistocene time. These maps suggest that the region occupied the northern margin of the Japan Sea sedimentary basin since Middle Miocene time, which became shallower with the passage of time by filling-up of sediments from the rapid upheaval of the eastern hinterlands. At the depositional stage of the Chikubetsu-Onishibetsu Formation (late Early Miocene to early Middle Miocene) the Japan Sea was formed and the sea area was being extended to the west of the region. At the stage of the Masuporo-Kotambetsu Formation (early to middle Middle Miocene) thick turbidite sediments were deposited with the upheaval of the central part of Hokkaido. Diatomaceous sediments were accumulated in a trough basin of N-S trend and a coastal environment was developed around the basin at the stage of the Wakkanai Formation (late Middle Miocene to early Late Miocene). The Koetoi-Embetsu Formation (latest Miocene to Early Pliocene) is composed mainly of continental shelf sediments and the Yuchi-Sarabetsu Formation (Late Pliocene to Pleistocene) is mainly of coarse sediments deposited in a coastal environment.