北海道石狩低地帯東縁部・栗山町および栗沢町の上部新生界とその堆積環境
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概要
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The Ishikari Lowland is situated between Western and Central Hokkaido. In Kuriyama and Kurisawa towns in the eastern marginal area of this lowland, thick marine Upper Cenozoic strata are distributed. They are a part of the thick sedimentary rocks widely distributed in an N-S direction in Central Kokkaido. These Middle Miocene Sedimentary rocks and deduced to have been deposited in a basin formed due to the collision and obduction of the Central Hokkaido Block to the Eurasian plate, which also resulted in the uplifted northern part of Central Hokkaido. The Hidaka Mountains, situated in the southern part of Central Hokkaido, were considered to have formed due to the collision between the Eastern Hokkaido Block and the southern part of the Central Hokkaido Block in Late Miocene time. Many previous sedimentological studies have been made in the northern part (for example, the Habaro district) and the southern part (for example, the Hidaka Coastal district) of the distribution of the thick sedimentary rocks. The study area is situated in the central part, which is in an important tectonic position between the Western and Central Hokkaido Blocks. In this study, I clarified Upper Cenozoic stratigraphy and gave consideration to the Late Cenozoic history of the basin through paleoenvironmental analysis and sedimentological study. The Neogene in this area is divided into the Takinoue, Kawabata, Iwamizawa, Oiwake and Kiyomappu Formations, in ascending order. The Takinoue Formation (Lower-Middle Miocene) is composed mostly of mudstone of deep sea origin, which overlies shallow marine sandstone. The Kawabata Formation (Middle Miocene) is composed of sediments of gravity flow origin, deposited in an N-S trending deep trough. The detrital material was derived mainly from the northern part of Central Hokkaido, as in the cases of the Kotanbetsu Formation in the Haboro district and the Ukekoi Formation in the Hidaka Coastal district. The Iwamizawa Formation (Middle Miocene) consists of bedded siliceous rocks, deposited in an N-S trending deep basin. The Oiwake Formation (Middle-Upper Miocene) consists mostly of sandy mudstone containing lenses of conglomerate, deposited in an open-deep basin, The clastic sediments were supplied mainly from the northern part of Central Hokkaido, as during deposition of the Kawabata Formation. Such provenance is different from that in the Hidaka Coastal district, where clastic sediments were supplied from the Hidaka Metamorphic Belt. This may be ascribed to submarine topography. These strata of Miocene age were deposited in a deep geosynclinal basin. The Kiyomappu Formation (Pliocene) consists of shallow marine tuffaceous sandstone. The Quaternry, consisting of terrace deposits including the Moseushi Formation, and alluvial deposits, rests on the Neogene with an unconformity.
- 地学団体研究会の論文
- 1990-09-25