<国立科博専報>足柄層群中部・上部層の貝化石群集について

概要

論文の詳細を見る
The molluscan fossils are abundant in the middle and upper parts of the Ashigara Group. The fauna in the middle part is dominated by the assemblage of the upper bathyal zone. It is characterized by Acila divaricata, Yoldia glauca, Macoma calarea, and is found in mudstone and fine-grained sandstone. The shallow sea molluscs are found in the conglomerate layers which are intercalated in the mudstone and sandstone. They are most probably transported into the basin from the nearby coastal area with gravels. In the southern area, shallow embayment assemblage composed of Meretrix lusoria, Dosinorbis japonicus and some other bivalves are seen. The assemblage is indicative of the existence of shallow area south of the upper bathval embayment. The lower horizon of the upper Ashigara Group comprises molluscan fossils of subtidal and intertidal species. Three shallow marine assemblages are recognized. They are the Meretrix lusoria-Dosinorbis japonicus assemblage, the Dosinella penicillata-Paphia euglypta assemblage, and the Grassostrea gigas-Trapezium liratum assemblage. The fossils indicate that the upper bathyal basin of the middle Ashigara Group were reclamated by sand and grevel, and changed into shallow embayment in the upper Ashigara age. The middle and upper Ashigara Group has been considered to be correlative with the Pliocene to lowest Pleistocene Kakegawa Group. However, the shallow sea molluscan fauna in the Ashigara Group does not contain any extinct species, while the shallow fauna of the Kakegawa Group is characterized by some extinct bivalves and gastropods. This is consistent with the occurrences of Umbonium costatum of the middle Plestocene type and proboscidian Parastegodon sp., both of which are known in the middle horizon of the Kazusa Group in the Boso Peninsula. Accordingly, the geologic age of the Ashigara Group may be the early to middle Pleistocene.
国立科学博物館の論文
1982-12-01

<国立科博専報>足柄層群中部・上部層の貝化石群集について

スポンサーリンク

概要

著者

関連論文

スポンサーリンク