茨城県大子町に露出する中新統内大野層の石灰質ナノ化石年代

Abstract

Calcareous nannofossil assemblages in mudstone samples from the Miocene Uchiono Formation exposed in Daigo Town, Ibaraki Prefecture, Japan, were examined for the depositional ages. Five samples obtained from four sites yielded calcareous nannofossils indicating CN3 or CN4 zones, which are dated to 17.65-13.60 Ma (early-middle Miocene). These results are consistent with previous studies of radiometric ages of pyroclastic rocks as well as diatom biostratigraphy.