Abstract
Investigation of four samples taken from an outcrop of the Ningyotoge Formation (Late Miocene to Pliocene), around the Ningyo Pass, between Okayama and Tottori Prefectures, Japan, revealed 101 taxa in 42 genera of fossil freshwater diatoms. Diatom assemblages of the four samples were dominated by centric diatoms (7 taxa) with a frequency of 56-82%, followed by araphid pennate diatoms (21 taxa) 7-18%, monoraphid pennate diatoms (13 taxa) 6-10% and biraphid pennate diatoms (60 taxa) 4-16%. Taxonomic information on 10 of the diatom taxa is reported here: Aulacoseira ambigua (Grunow) Simonsen, Aulacoseira sp., Discostella sp., Cocconeis placentula Ehrenb. var. lineata (Ehrenb. ) Van Heurck, Didymosphenia sp., Epithemia cistula (Ehrenb. ) Ralfs, Gomphonema sp., Melosira undulata (Ehrenb. ) Kütz., Synedra capitata Ehrenb. and Tetracyclus stellare var. eximius (Hérib. & Perag. ) Hust. Of particular interest is the presence of a Didymosphenia taxon, indicating that a cool temperate climate existed during the formation of the deposit. Six taxa of Tetracyclus occurred in the fossil diatom assemblage.
