Abstract
For paleoenvironmental reconstruction using diatom analysis, it is necessary to investigate the formational process of dead diatom assemblages by the transportation and sedimentation of diatom frustuls.
In order to examine taphonomic processes of diatom frustuls, and to establish new diatom environmental indicators, this paper presents findings on the relationship among distribution, size (length) of diatom frustules, grain size of deposits, LOI (Loss on Ignition), and their seasonal variations in a tidal area of the Obitsu river, Chiba Prefecture.
The results are as follows. (1) Distribution and abundance of living diatom cells relates to LOI, but abundance of dead diatoms relates to silt contents of deposits in all seasons. (2) Diatom frustules (mean length about 5.9φ and more) are usually transported and deposited as silt-size grains by tidal flows, and abundance of allochthonous dead diatoms increases in the sedimentary environment composed dominantly of silt. (3) Four species of “diatom environmental indicators” are more utilizable, and eight species are proposed to be new diatom environmental indicators.
Thus, it is significant to distinguish allochthonous dead diatoms from diatom assemblages, and possible to improve new diatom environmental indicators by the combined estimation of size characteristics—for example length of diatom frustules—and sedimentary properties such as grain size in the modern tidal environment.
