珪藻化石群集による古奥東京湾の塩分濃度の推定

抄録

A method for estimation of paleo-salinity based on diatom assemblages is presented in this paper. Diatom environmental indicators (KOSUGI, 1988b), characterized by specific ranges of salinity, were utilized to estimate paleo-salinity. As a result of comparing the estimated salinity with real salinity in present environments, both salinity were seen to correspond if the estimated salinity was recognized as conforming with indicators prescribing an appearence ratio greater than 5%.
As an application of this method, the paleo-salinities at 6 localities from the Paleo Oku-Tokyo Bay were estimated. As a result, it was thought that in the earlier stage of the Jomon Transgression (Holocene Transgression) paleo-salinity rapidly increased, while at the later stage it decreased slowly. The upper limits of the marine sediments were identified as +2-3m in small valleys in sourrounding terraces and +1-2m in the Nakagawa lowland.
Moreover, allochthonous cells in fossil assemblages were identified using this method. If the species groups having ranges outside the estimated range of salinity are recognized as allochthonous, more than a few allochthonous groups in a fossil assemblage are descriminated.