札幌市街域における150m掘削コアの第四系層序  [in Japanese] Quaternary stratigraphy of the 150 m core in the central part of Sapporo, Japan  [in Japanese]

札幌市市街域の北海道大学構内で,1981年の掘削で得られた150mコアの第四系層序を明らかにするために,^<14>C年代測定,堆積相解析,火山灰分析,花粉分析,珪藻分析,放散虫分析を行った.孔内地質はHU-1層〜HU-9層に区分され,分析結果に基づく野幌丘陵との地層対比では,HU-1層〜HU-3層(深度150〜75m)は前・中期更新世の下野幌層,HU-4層〜HU-5層(深度75〜35m)は後期更新世のもみじ台層,HU-6層(深度35〜34m)は後期更新世の小野幌層,HU-7層〜HU-8層(深度34〜7.8m)は後期更新世の札幌扇状地堆積物,HU-9層(深度7.8〜Om)は完新統に相当することが明らかになった.最終間氷期堆積物であるHU-4層〜HU-5層からは,寒冷期や温暖期が確認され,今後の石狩低地帯南部の第四系との詳細な対比の可能性が生じた.既存井との地層対比では,150mコアの深度130m(標高-119m)付近に挟在する下野幌層相当層中の泥炭は,隣接する2本の井戸の標高-110m付近に認められる亜炭質層と連続し,更には石狩海岸平野下の下野幌層相当層の標高-102〜-126mに挟在する泥炭に対比される.

^<14>C dating, sedimentary facies analysis, volcanic ash analysis, pollen analysis, diatom analysis and radiolaria analysis were carried out to clarify the Quaternary stratigraphy on the 150 m core, drilled in 1981, in the campus of Hokkaido University, central part of Sapporo. Our investigation leads to the following conclusions. 1) The core is divided into nine formations, HU-1 to HU-9. The HU-1 to the HU-3 in 150 - 75 m depth are correlated to the Shimonopporo Formation of the early to middle Pleistocene, the HU-4 and the HU-5 in 75 - 35 m depth to the Momijidai Formation of the late Pleistocene, the HU-6 in 35-34 m depth to the Konopporo Formation of the late Pleistocene, the HU-7 and the HU-8 in 34 - 7.8 m depth to the Sapporo Fan Deposits of the late Pleistocene, the HU-9 in 7.8 - 0 m depth to the Holocene. 2) Identification of the cold stage and warm stage in the HU-4 and HU-5, last interglacial stage deposits, causes the possibility of accurately comparing to the deposits in the southernmost part of Ishikari Depression. 3) Peat bed intercalated in 130 m depth, 119 m below sea level, in the correlative of Shimonopporo Formation of the core is correlated to the peaty deposits which exist at about 110 m below sea level in the nearby two boreholes, and peat beds which intercalated under the Ishikari Coastal Plain within the range from 102 m to 126 m below sea level in the cor- relative of the Shimonopporo Formation.