北海道における貝塚の生物群集

特に縄文海進に関連して

抄録

From the analysis of molluscan assemblages found in numerous shell mounds, the following conclusions are drawn as to the sea conditions around Hokkaido in Post-Glacial Epoch. In the late Earliest to the middle Early Jomon cultural age (Ca. 5,000-6,000 years B.P.) such warm sea molluscs Rapana thomasiana, Meretrix lusoria Mactra veneriformis were widely distributed along the coast line of Hokkaido. Therefore, it is assumed that the surface temperature of the sea around Hokkaido at that time must have been 8℃ at the minimum, and 23℃ or more at the maximum. Then the sea level reached the maximum height of 3 m± resulting the so-called Jomon Trangression. From the late Early to the middle Middle Jomon cultural age (Ca. 4,000-5,000 years B.P.) the molluscan assemblages in various shell mounds reveal discrepancy between the Japan sea side of the island. On the Japan sea side, molluscan elements were similar to those of the preceding age. While on the Paific side the dominance of cold water elements became notable. Judged from this evidence, the sea temperature might have remained more or less the same with that of the preceding age on the Japan sea side, where as it might have been colder than before on the Pacific side, though it still was definitely higher than the present day sea temperature of the same region. As to the height of sea level of this age we have not sufficient data to confirm, but it was presumably a little lower than that of the preceding age. From the late middle, or the Late Jomon cultural age onward the molluscan assemblages became essentially the same reflecting the present distribution of molluscs in Hokkaido, where the sea conditions also became similar to those of the present.