Shallow marine diatom assemblage change during the past million years in the Nishimikawa Plain, Aichi Prefecture, Japan

Abstract

Diatom assemblages recovered from three drilling cores, GS-HKN-1, GS-NSO-2 and TK No.1 cores, drilled in the Nishimikawa Plain, Aichi Prefecture, Japan, are investigated. The diatom assemblages from each core comprise a series of repeating assemblages dominated by marine and brackish-water diatoms and freshwater diatoms. Diatom zones were defined in each core (zones HKN1-1 to 8, NSO2-1 to 4 and TK1-1 to 6, respectively, from lower to upper), and the diatom assemblages in each zone were documented and their depositional environments were also estimated. The age of the marine intervals, which consist mainly of marine and brackish-water diatom assemblages, and their correlation with oxygen isotope stages (MIS) indicate that at least nine marine intervals are intercalated in the sediments of the Nishimikawa Plain over the past million years. The last occurrence of Cyclotella stylorum in the late Early Pleistocene, Lancineis rectilatus in MIS15 or MIS17, Diploneis cf. bombus in MIS11, and Paralia fenestrata only occurs above MIS19. The biostratigraphy of these diatom fossils can provide a useful stratigraphic reference for the Pleistocene in this area. Microscopic photographs of the key diatom fossils are illustrated, together with a list of references and illustrations for the basis of identification.