The Ishikari coastal plain is situated in the northwestern end of the so-called Sapporo-Tomakomai Lowland in Hokkaido, and bears such topographic features as coastal sand dunes, ridged beach plain, the older dunes and back marshes. The present report intends to clarify sea levels, stratigraphy and sedimentary process of deposits after the Würmian glacial maximum (20, 000-18, 000 years B.P.). At first buried landforms of the area in the Würmian glacial maximum are considered on the basis of many boring data. Consequently the shape and the depth of four buried terraces deposits (Bt1-Bt4), palaeo-delta and buried valleys have been discriminated. Among them Bt1 was formed before the eruption of Shikotsu volcano (caldera). Bt2-Bt4 and palaeo-delta deposits were formed after the Paudorf interglacial epoch untill the Würmian glacial maximum. Whereas gravel beds of buried valleys were flood plain deposits of old rivers in the Würmian glacial maximum. Estimation of sea level at that time of glacial age is difficult owing to that the Ishikari coastal plain was a land area then. However it is almost certain that the sea level was at least 65 meters below the present one. Then, the sea gradually invaded into the land, following transgression after the Würmian glacial maximum, and palaeotopographic relief was completely buried by later deposits, of which the upper part is characterized by the presence of black, soft clay. Later temporary regression caused a sand bar linking mountains southwest to the Ishikari hills in the northeast. Finally it developed to a sand-gravel barrier at the place of Momijiyama sand dune, and it created a big change in sedimentary environments of the area. Namely thereafter, swampy deposits were developed in the inland parts of the sand-gravel barrier, and rows of beach ridges were developed in seaward. The Bannaguro lowland formed by the development of continuous sedimentary processes when the sea level was 4-4.5 meters higher than the present one. From radiocarbon dating of marine shells contained in the deposits of beach ridges, it was clarified that the age of high sea level (4-4.5 meters) continued from 5, 800 to 2, 000 years B.P. Then followed a sudden lowering of sea level down to the present one and we see the present topography.
In order to investigate the distributional history of Cryptomeria japonica in the Late Quaternary, the pollen analyses were made on six moors: Utonaito and Konuma moors in Hokkaido, and Narugo, Moniwa-Takada, Menuma and Hoshojiri moors in Tohoku district. The results show that Cryptomeria pollen increase around 2, 000y.B.P. in the investigated area except Hokkaido of the northern Japan. Cryptomeria japonica has never distributed in the Late Holocene, at least, in Hokkaido. Further, as a result of investigating many data of Tohoku district, the increasing ages of Cryptomeria pollen are 1, 500-4, 500y.B.P. in each region. From the fact, it is suggested that Cryptomeria japonica doesn't spread uniformly all over the place. Roughly speaking, from these facts and the previous many data, there is the tendency that the increasing ages of Cryptomeria pollen are newer in the north than in the south of Japan. So, it seems that Cryptomeria japonica spread from south to north after the Late Glacial Age.
This preliminary report gives the distribution of the active faults, their geomorphological features and the relationship between the parasitic eruption centers and the active faults found on the west flank of the Aso caldera. 1) Many active faults are distributed on the west flank of the Aso caldera. NE trending faults dip north with right-lateral displacement. They are geomorphological manifestations of the Oita-Kumamoto tectonic line. 2) Rate of vertical displacement of the Futagawa-fault, a principal fault in the studied area, is 1.7 to 0.6mm/y. for recent 350, 000 years as indicated by the displacement of the Aso pyroclastic flow deposits. 3) The Hinagu-fault joins the Oita-Kumamoto tectonic line near the southern end of the Futagawa-fault. 4) Lowland along Kiyama to Kashima formed by the active faulting is named Kiyama-Kashima graben. Narrow graben is also developed along the Hinagu-fault. 5) It is noteworthy that the grabens are situated right outside of bending of Southwest Honshu arc from SW to SSW trend, the trend of the Ryukyu arc. 6) Eruption centers of the parasitic volcanoes of the Aso caldera are situated at local tensional stress fields formed by right-lateral faulting of echelon arrangement active faults.