The Kuji River, which flows from southern Fukushima Prefecture to northern Ibaraki Prefecture, traverses the northern Kanto Mountains and the northeastern Kanto Plain. The ages of terraces along the Kuji River provide information on the uplift of the northern Kanto Mountains and the difference in the amount of tectonic uplift between the mountains and the plain. In this study, we newly discovered Daisen- Kurayoshi tephra (DKP) in a fluvial terrace deposit at Minamitage, Daigo Town. The tephra retains volcanic glass, whose refractive index, major chemical composition, and petrological characteristics are consistent with reported data for DKP tephra. Based on the terrace age and the height difference between the present riverbed and the terrace surfaces, it is possible to compare the terraces along the Kuji River in the northern Kanto Mountains and in the Kanto Plain (eastern Urizura Hills). The results suggest that there has been no significant difference in tectonic uplift between these regions for at least the last 60,000 years.

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.