北海道東部,根釧原野の中・下部更新統

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In the Konsengenya Plain, Pleistocene formations are extensively distributed. The Lower to Middle Pleistocene formations yield fossils of mollusca, pollen, diatom, and are divided into the Furenko Formatoin, the Bekanbeushigawa Formation of the Kushiro Group and the Konsen Formation in ascending order. The Furenko Formation is mainly composed of silt and silty sand. The Formation yields mollusca of Acila nakazimai, reported in the Pliocene to Lower Pleistocene. Diatom of Denticulopsis seminae var. fossilis is found in this formation. KOIZUMI (1985) reported the diatom zone of this species indicating the age of 1.89-2.50 Ma. The pollen fossils of Cryptomeria, Picea and Betula are dominantly included; the composition indicates the warm humid climate. The Bekanbeushigawa Formation consists mainly of pumiceous gravel, sand, tuffaceous silt and peat. Some species of mollusca are regarded as the cold current type. The pollen fossils of Picea, Abies, Tsuga and Larix are dominantly included; the composition indicates the vegetation of the coniferous forest in subpolar zone. The fossil diatoms regarded as fresh water species are dominantly included in this formation. The Konsen Formation is composed mainly of sand, silt and gravel. The fossils of mollusca of warmer species are remarkably included. The composition of the pollen fossils indicates the vegetation of broad-leaved forest in temperates zone. The diatomaceous fossils are composed of brackish〜sea water species and fresh water ones. According to the above results, the geological age of those formations is as follows; the Furenko Formation belongs to Upper Pliocene to Lower Pleistocene age, the Bekanbeushigawa Formation Lower to Middle Pleistocene age, and the Konsen Formation Middle Pleistocene age.
地学団体研究会の論文
1986-11-25

北海道東部,根釧原野の中・下部更新統

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