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K-Ar and fission track ages of the Kt-1 Tuff in the Miocene marine sequence in the Tanagura area, Northeast Japan

K-Ar and fission track ages were determined for the Kt-1 Tuff interbedded in the lowest part of the Miocene Kubota Formation in the Tanagura area. A K-Ar age of the Kt-1 Tuff was determined as 10.6±0.2 Ma on biotite. A fission track age was also determined using zircon as 10.7±0.2 Ma. Both ages well coincide with each other, which suggests that the obtained ages represent the eruption age of the Kt-1 pyroclastics. Reported results of the biostratigraphic analysis are concordant with the newly obtained radiometric ages.