Age and paleoclimatic implication of middle to upper Miocene plant‐bearing strata in the southern Kanazawa area, Ishikawa Prefecture, Central Japan, based on refined Neogene palynostratigraphy in the Hokuriku district

Abstract

Abstract13–8 Ma (middle to late Miocene) is a key period for understanding how the unique vegetation was established in Japan. Palynostratigraphy is useful for estimating the ages of plant‐bearing strata deposited in shallow‐marine and non‐marine environments, but has low temporal resolution for this key period in Japan. We compiled Neogene and early Quaternary palynological records for the Hokuriku district of Central Japan to clarify palynostratigraphic events that may improve the temporal resolution. Our results showed that palynoassemblages changed considerably during 10–6.4 Ma in the Hokuriku district, following a relatively stable period during 13–10 Ma. We found that evergreen Quercus abundance increased at 11.5–10 Ma. We used these palynostratigraphic signatures, along with other biostratigraphic markers, to infer the ages of the Miocene plant‐bearing Saikawa and Koderayama Formations in the southern Kanazawa area of Ishikawa Prefecture in the Hokuriku district. The ages of the Saikawa and Koderayama Formations were inferred as ~13 and 10–6.4 Ma, respectively. The palynoflora of the Koderayama Formation shows floristic similarity to that of present south China, implying that the unique flora of Japan established after the age of the Koderayama Formation.