いわゆる"西谷砂層"の一部から産する軟体動物化石の混合の型について

抄録

A great deal of marine molluscan fossils is contained in the Lower or Middle Pleistocene Nisiyatu sand developed in the northern part of the Boso Peninsula, South Kanto, Japan. The molluscan fossil-coenosis consists mainly of two elements, which are euneritic and subneritic-bathyneritic. The former element is composed of both Kurosio and Oyasio types, and the latter is composed mainly of Kurosio type.
Judging from the state of preservation of each fossil, the euneritic Kurosio element is translocated by bottom-current into deep sea-bottom and mixed with subneritic-bathyneritic element, but the so-called euneritic Oyasio and the subneritic-bathyneritic Kurosio elements may be considered to be para-autochthonous. Therefore, it can be easily understood that the so-called eu-neritic Oyasio element in this molluscan fossil-coenosis was the subneritic-bathyneritic dwellers when the Nisiyatu sand was deposited. In other words, the mixture of Kurosio and Oyasio types in the euneritic element is not caused by increase and decrease of warm and cold currents.