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, Hk
1, Hk
2 and Hk
3, based on the facies distribution. The upward shallowing succession of Hk
1 and Hk
2 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 Hk
2 in the western limb and only the uppermost of Hk
2 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 Hk
3 distributed widely in both limbs. The upper two parasequences of the three recognized in Hk
3 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).
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