Distinguishing reworked diatoms derived from Neogene marine strata in modern coastal assemblages for understanding taphonomic processes and reconstructing Holocene paleoenvironments in the Tokachi coastal area, Hokkaido, Japan

Abstract Identification of autochthonous, allochthonous, and reworked (derived fossil) taxa in diatom analyses is of fundamental importance for understanding how taphonomic processes affect diatom assemblages and for estimating paleoenvironments in coastal areas. To characterize modern and Neogene diatom assemblages, we surveyed the distributions of modern diatom assemblages and of Neogene fossil diatom assemblages in the Toberi River area, eastern Hokkaido, Japan. Then, on the basis of these results, we analyzed two cores collected near the Toberi River mouth and examined changes in the fossil diatom assemblages during the late Holocene. The results showed that not only allochthonous and extinct diatom taxa, but also extant taxa that have persisted over an extended geological time period, should be excluded when diatom assemblages are analyzed to reconstruct Holocene paleoenvironments in this area.