福井県大飯郡高浜町地下の自然貝層--貝化石群集の解析による古環境の復元と14C年代

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Holocene shell beds were discovered in the underground of Takahama-cho, Oi-gun, Fukui Prefecture. The sequence of the Holocene strata occurs between 2 and 6m in depth, and was divided into six stratigraphic horizons on the basis of the characteristics of lithology and fossil molluscan assemblages, foraminiferas and ostracodas. In this study, 14C ages of every representative molluscan assemblage were determined. The results indicated that the molluscan assemblages are 1, 000 to 5, 000 years old. According to the shell-assemblage results from synecological analysis, the following paleoenvironmental transitions were clarified: the Takahama area was a mud-depositing intertidal zone 5, 000 years ago, a sand and mud-depositing shallow-water bottom during a minor transgression 4, 000 years ago, an intertidal zone due to gradual lowering of the sea level 2, 000 years ago, a brackish water area 1, 000 years ago, and a swamp-like land influenced by rivers since that time. Assemblage analysis of foraminiferas and ostracodas gave us very similar results.A 4, 000 to 2, 000 year-old molluscan assemblage contains many subtropical shells such as Clypeomorus coralium, Plicarcularia bellula, Tegillarca granosa, Anomalocardia (Anomalodiscus) squamosa, which cannot be found in the present Wakasa Bay. The analysis of the fossil molluscan asseblages and determination of 14C ages made it clear that a minor transgression took place 4, 000 years ago and that the subtropical shells, which are considered to have been extinct 4, 000 to 5, 000 years ago in the Kanto region, survived in the Takahama area until 2, 000 years ago.
日本第四紀学会の論文

福井県大飯郡高浜町地下の自然貝層--貝化石群集の解析による古環境の復元と14C年代

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