北海道白亜系函淵層群の堆積相と堆積シーケンス
空知背斜地域
1993 年 38 巻 38 号 p. 45-52
詳細
1993 年 38 巻 38 号 p. 45-52
The Hakubuchi Group is the uppermost unit of the Yezo Supergroup, a forearc basin sediment distributed along the meridional zone of Hokkaido, Japan. The group in the Sorachi Anticline represents the western marginal facies of the basin, showing conspicuous lateral facies changes. It is subdivided into three formations, Hk1, Hk2 and Hk3, based on the facies distribution. The upward shallowing succession of Hk1 and Hk2 in the eastern limb of the anticline, which is composed of inner shelf to delta plain facies through shoreface, foreshore and beach facies, is interpreted to be a lowstand delta on a conformable sequence boundary. The massive conglomerate facies constituting very thick Hk2 in the western limb and only the uppermost of Hk2 in the eastern limb, may be a transgressive systems tract. The base of the conglomerate in the wester limb corresponds to an erosional sequence boundary. A highstand systems tract is represented by Hk3 distributed widely in both limbs. The upper two parasequences of the three recognized in Hk3 had been partly eroded away under a sequence boundary (clinounconformity) with the Eocene coal measures, Ishikari Group. Therefore, the Hakobuchi Group constitutes a depositional sequence during 10m.y. (Lower Camapanian-Lower Maastrichtian).
