Miocene Diatom Biostratigraphy of Onshore Sequences on the Pacific Side of Northeast Japan, with Reference to DSDP Hole 438A (Part 1)

Abstract

Taxonomic investigations of the genus Denticulopsis are attempted through observations aided by both optical and scanning electron microscopes. Species belonging to the genus Denticulopsis are classified into six groups on the basis of structure of the valve face and the presence or absence of secondary pseudosepta. A new taxonomic formulation is proposed in order to describe a diatom frustule and its components by taking representative Denticulopsis species. A comparative study of morphology of D. praedimorpha and D. dimorpha indicates that a structural difference of the connecting band provides the most easily recognizable character to differentiate these two species. Three trends in the morphological development of this genus are discussed. A new diatom species Denticulopsis katayamae is described and this species has been found to be useful for biostratigraphic studies of Miocene sequences of Northeast Japan